Method of testing assembled internal combustion engine

ABSTRACT

A method of testing the assembled state of an internal combustion engine and quickly and accurately judging whether there is at least one fault with the assembling of the engine. While an exhaust-valve side space ( 100 ) is closed and a crank shaft ( 18 ) is rotated at a constant speed, the pressure in the exhaust-valve side space and the pressure in a surge tank ( 96 ) are detected by pressure sensors ( 106, 98 ), respectively. The assembled state of an engine ( 90 ) is tested based on the predetermined conditions of the detected two pressures. Those predetermined conditions may be the crank-shaft angles when the two pressures take respective maximal values, the crank-shaft angles when the two pressures change from their constant states to their increasing or decreasing states, etc. Based on those values, incorrect phases of crank and cam pulleys, incorrect clerances of intake and exhaust valves, missing of a compression ring, etc. can be identified.

TECHNICAL FIELD

[0001] The present invention relates to a method of checking or testingthe assembled state of an internal combustion engine.

BACKGROUND ART

[0002] When the assembling of an internal combustion engine(hereinafter, referred to as the “engine”) finishes, it is necessary tojudge whether there is a fault with the assembling of the engine, suchas missing of any part of the engine, or asynchronism of respectiveoperations of two or more parts of the same. If the engine has a fault,it cannot perform as designed. One example of the assembled enginetesting method is disclosed in U.S. Pat. No. 5,355,713. In the disclosedmethod, an assembled engine is rotated in a “cool” state in which nofuel is fired, a pressure waveform is obtained from an exhaust-valve orintake-valve side space of the engine, and the obtained pressurewaveform is compared with a reference pressure waveform which isobtained in advance from a normal engine. Thus, whether or not there isa fault with the assembling of the engine is judged. The U.S. patentdiscloses the technique of comparing a characteristic of the obtainedwaveform with a corresponding characteristic of the reference waveform.The characteristic may be the amplitude of at least one of a (positive)pressure pulse and a vacuum (negative pressure) pulse contained in eachpressure waveform. In addition, the U.S. patent discloses the techniqueof judging that an assembled engine has a fault if the pressure in theexhaust-valve side space of the engine (hereinafter, referred to as the“exhaust pressure”) does not exceed a reference value at a predeterminedangular phase of a crank shaft of the engine (hereinafter, referred toas the “crank-shaft (CS) angle”) where the exhaust pressure would exceedthe reference value if the engine were normal. That is, the enginetesting method disclosed in the U.S. patent consists in comparing ameasured characteristic value of exhaust or intake pressure of anassembled engine, such as maximal or minimal value or a valuecorresponding to a particular CS angle, with a reference value obtainedfrom a normal engine.

[0003] The U.S. patent teaches finding a fault with an assembled enginebased on a pressure waveform obtained from either one of theexhaust-valve or intake-valve side space of the engine. However, itfails to teach finding a fault based on respective pressure waveformsobtained from the exhaust-valve and intake-valve side spaces of theengine. In addition, if the disclosed method finds a fault, it ends.Therefore, if an assembled engine has different sorts of faults, themethod cannot find those faults.

DISCLOSURE OF INVENTION

[0004] It is therefore an object of the present invention to provide anassembled engine testing method which is different from that disclosedin the above-identified U.S. patent.

[0005] According to a first aspect of the present invention, there isprovided a method of testing an assembled internal combustion enginehaving an intake valve and an exhaust valve, being characterized byrotating the assembled engine, measuring a timing of occurrence of atleast one predetermined condition of a pressure in at least one of anexternal intake-valve side space which communicates with the intakevalve and an external exhaust-valve side space which communicates withthe exhaust valve, and judging, based on the measured timing, whetherthere is at least one fault with the assembling of the engine.

[0006] In the testing method in accordance with the first aspect of theinvention, the timing of occurrence of the at least one predeterminedcondition of the pressure in the intake-valve side space or the externalexhaust-valve side space (hereinafter, referred to as “the intakepressure” or the “exhaust pressure”) changes depending upon the changingpressure in a cylinder (hereinafter, referred to as the “cylinderpressure”) in which a piston reciprocates linearly and the opening andclosing timings of the intake and exhaust valves. The cylinder pressureincreases as the piston moves up toward its top dead position, anddecreases as the piston moves down toward its bottom dead position. Inthe reciprocating engine, after the intake and exhaust valves close,first, the exhaust valve starts opening and subsequently the intakevalve starts opening. After the exhaust valve closes, the intake valvecloses. During each cycle, if, e.g., the timing of commencement ofopening of the intake valve is earlier (i.e., corresponds to a smallerCS angle) than a reference timing obtained from a normal engine, theexhaust pressure takes a maximal value smaller than a reference valueobtained from the normal engine and takes a less time to reach themaximal value. To the contrary, if the timing of commencement of openingof the intake valve is later (i.e., corresponds to a larger CS angle)than the reference timing obtained from the normal engine, the exhaustpressure takes a maximal value greater than the reference value andtakes a more time to reach the maximal value. Therefore, if, e.g., thetiming when the exhaust pressure takes a maximal value is known, therelationship between the opening and closing timings of the intake valveand the CS angle is known. Thus, it can be judged that the assembledengine has the assembling fault of an incorrect phase difference betweena crank shaft and a cam shaft. In addition, if, e.g., the opening andclosing timings of the exhaust valve change relative to the CS angle,the change influences the intake pressure. Thus, the fault of incorrectphase difference between the crank and cam shafts can be identifiedbased on the timing of occurrence of at least one predeterminedcondition of the intake pressure. In this way, it is possible to judgewhether there is at least one fault with an assembled engine, based onthe timing of occurrence of one or more predetermined conditions of theintake pressure and/or the exhaust pressure, without having to take theengine apart. The present testing method does not exclude finding anassembling fault by taking into account an intake or exhaust pressurevalue corresponding to the predetermined condition. For example, anexhaust pressure value at the timing when the exhaust valve startsopening, a maximal value of the exhaust pressure, etc. may be taken intoaccount. The assembled engine may be rotated in a “hot” state, i.e., byfiring of fuel therein, or in a “cool” state, i.e., by being connectedto a separate rotating device and compulsorily rotated by the device.Generally, the “cool” test is easier than the “hot” test. In the hottest, it is cumbersome to supply fuel to the engine and treat theexhaust gas emitted therefrom. In addition, in the “hot” test, thepressure signals obtained from the intake-side and exhaust-side spacescontain more noise. The “cool” test is free from those problems, andaccordingly can be carried out more easily.

[0007] According to a preferred feature of the first aspect of theinvention, the judging step comprises comparing the measured timing witha reference timing and judging, based on the comparison result, whetherthere is at least one fault with the assembling of the engine. Thereference timing may be a timing which is actually measured from anormal engine having no assembling fault, or may be a timing which isprescribed by a designer. An incorrect phase of a crank shaft may becaused by an incorrect relative phase between the crank shaft and acrank pulley due to inappropriate attachment of the pulley to the shaft,an incorrect relative phase between the crank pulley and a timing beltor chain due to inappropriate engagement thereof, etc. An incorrectphase of a cam shaft may be caused by an incorrect relative phasebetween the cam shaft and a cam pulley due to inappropriate attachmentof the cam pulley to the cam shaft, an incorrect relative phase betweenthe cam pulley and a timing belt or chain due to inappropriateengagement thereof, etc. As will be described later on the preferredembodiments, the incorrect phase of the cam shaft may also be caused byan incorrect relative phase between a drive gear attached to one of anintake cam shaft for operating the intake valves and an exhaust camshaft for operating the exhaust valves, and a driven gear attached tothe other cam shaft. The timing of occurrence of the predeterminedcondition of the exhaust or intake pressure discontinuously changes dueto the presence of each of the above faults, because the amount ofdeviation of the incorrect phase of the crank pulley, etc. from itscorrect phase stepwise changes. Similarly, the timing of occurrence ofthe predetermined condition discontinuously changes due to missing of acompression ring. Therefore, the reference timing with which themeasured timing is compared may be a timing of occurrence of thepredetermined condition which is measured from one or more normalengines each having no assembling fault. Therefore, if the differencebetween the measured timing and the reference timing falls in areference range, the assembled engine may be judged as normal, i.e.,having no assembling fault. On the other hand, the timing of occurrenceof the predetermined condition continuously changes due to the presenceof an incorrect intake-valve or exhaust-valve clearance. Therefore, ifthe clearance of an intake or exhaust valve falls in a reference range,the valve may be judged as normal. In the last case, the reference valuewith which the measured value is compared corresponds to every valuewithin the reference range. In any case, the reference value is used asa criterion for distinguishing an engine having at least one fault froman engine having no fault. Therefore, whether there is at least onefault with an assembled engine can be judged quickly and easily bycomparing the measured timing of occurrence of the predeterminedcondition, with the reference timing.

[0008] According to another feature of the first aspect of theinvention, the measuring step comprises measuring at least one of afirst timing when the exhaust pressure in the exhaust-valve side spacetakes a maximal value; a second timing when the exhaust pressure changesfrom a first decreasing state to a constant state in which the exhaustpressure does not change as time elapses; a third timing when theexhaust pressure changes from the constant state to a second decreasingstate; a fourth timing when the intake pressure in the intake-valve sidespace takes a maximal value; and a fifth timing when the intake pressurechanges from a constant state in which the intake pressure does notchange as time elapses, to an increasing state. The first to fifthtimings are very reliable for finding at least one assembling fault,because at each of those timings the exhaust or intake pressuresignificantly changes. Therefore, each of those timings can be measuredwith high accuracy, and one or more faults can be found with highreliability.

[0009] According to another feature of the first aspect of theinvention, the judging step comprises identifying at least one faultwith the assembling of the engine based on at least one of a positive ornegative sign and an absolute value of a difference between at least onemeasured timing out of the first to fifth timings and a correspondingone of a first, a second, a third, a fourth, and a fifth referencetiming.

[0010] According to another feature of the first aspect of theinvention, the judging step comprises identifying at least one faultwith the assembling of the engine based on a combination of a pluralityof measured timings out of the first to fifth timings each of whichmeasured timings is different from a corresponding one of a first, asecond, a third, a fourth, and a fifth reference timing.

[0011] According to another feature of the first aspect of theinvention, the at least one fault comprises at least one of an incorrectclearance of the intake valve; an incorrect clearance of the exhaustvalve; an incorrect relative phase between a crank shaft and a camshaft; and a missing of a compression ring. The four assembling faultsoccur most frequently. As will be described later by reference to thepreferred embodiments of the invention, it is possible to identify atleast two faults out of those four faults, based on the measured timingof at least one predetermined condition of the intake pressure and/orthe exhaust pressure. Since those faults actually occur frequently inassembly lines, it is very efficient to be able to find one or more ofthose faults without having to take the engine apart.

[0012] According to another feature of the first aspect of theinvention, the incorrect relative phase between the crank shaft and thecam shaft comprises at least one of an incorrect relative phase betweenthe crank shaft and a crank pulley; an incorrect relative phase betweena cam pulley and the cam shaft; and an incorrect relative phase betweena drive gear and a driven gear.

[0013] According to another feature of the first aspect of theinvention, the testing method further comprises the step of closing atleast one of an exhaust-valve side passage which connects between theexhaust valve and an exhaust manifold and an intake-valve side passagewhich connects between the intake valve and an intake manifold, whereinthe at least one of the external exhaust-valve side space and theexternal intake-valve side space comprises at least one of anexhaust-valve side portion of the closed exhaust-valve side passage andan intake-valve side portion of the closed intake-valve side passage. Inthis case, the reliability of the engine testing method is improved. Itis possible to measure the exhaust or intake pressure without having toclose the exhaust-valve side passage which connects between the exhaustvalve and the exhaust manifold, or the intake-valve side passage whichconnects between the intake valve and the intake manifold. However, inthe case where the exhaust-valve side passage and/or intake-valve sidepassage are/is closed, it is possible to detect accurately a change ofthe exhaust or intake pressure which results from the presence of one ormore assembling faults, and accurately measure the timing of occurrenceof at least one predetermined condition of the exhaust or intakepressure. Thus, the present testing method enjoys an improvedreliability. In this case, it is preferred to carry out the testingmethod before the exhaust manifold and/or the intake manifold are/isattached to the engine.

[0014] According to another feature of the first aspect of theinvention, the at least one of the external intake-valve side space andthe external exhaust-valve side space comprises the exhaust-valve sidespace which comprises an an exhaust-valve room and an exhaust manifoldwhose outlet is closed. In each cycle of operation of an engine having aplurality of cylinders, the opening and closing of the exhaust valve orvalves of each of the cylinders sequentially occur at a regular intervalof timing. As will be described later on the preferred embodiments, ifthe pressure in a single space provided by the exhaust-valve room and aninner space of the exhaust manifold is detected, then it can be judgedwhether there is at least one fault with each cylinder of the engine.Since in this case the testing method can be carried out after theexhaust manifold has been assembled, the exhaust pressure of eachcylinder can be detected more easily.

[0015] According to another feature of the first aspect of theinvention, the at least one of the external intake-valve side space andthe external exhaust-valve side space comprises an internal space of asurge tank. In each cycle of operation of an engine having a pluralityof cylinders, the opening and closing of the intake valve or valves ofeach of the cylinders sequentially occur at a regular interval oftiming, like the opening and closing of the exhaust valve or valves ofeach cylinder. As will be described later on the preferred embodiments,if the pressure in the inner space of the surge tank is detected, thenit can be judged whether there is at least one fault with each cylinderof the engine. Since in this case the testing method can be carried outafter the intake manifold and the surge tank have been assembled and thenumber of pressure sensors employed can be minimized, the intakepressure of each cylinder can be detected very easily.

[0016] According to another feature of the first aspect of theinvention, the judging step comprises identifying at least two faultsout of a plurality of faults of the engine which result from theassembling thereof. In the case where a plurality of assembling faultsoccur to a single engine, the testing method in accordance with thefirst aspect of the invention may identify only the presence of one ormore faults out of the plurality of faults. Otherwise, if it identifiesof what kind is one fault found, then the test may be over with theidentified fault being displayed. In contrast, in the testing method inaccordance with the present feature, at least two faults aresimultaneously identified. In the case where only the presence of one ormore faults is identified, an operator must take the engine apart andidentify the fault or faults. In the case where the engine test isterminated when a fault is identified, the operator must correct thefault displayed and again carry out the same test on the engine foridentifying another possible fault and correcting the second fault. Ineither case, it takes a long time to remove the fault or faults from theengine. In contrast, if at least two faults out of the plurality offaults with the engine can be simultaneously identified, thoseidentified faults can be simultaneously removed. If all the faults withthe engine can be simultaneously identified, all those faults can besimultaneously removed. The last case is ideal. However, it is notessentially required that all the faults with the engine besimultaneously identified. It is sufficiently efficient to identifysimultaneously at least two faults out of the plurality of faults withthe engine. In addition, if the total number of faults which the enginemay have with any possibility can be limited or reduced to a smaller onebased on the measured timing, the time needed to identify the fault orfaults with the engine can be accordingly reduced.

[0017] According to another feature of the first aspect of theinvention, the at least one predetermined condition of the pressure canoccur at a plurality of timings corresponding to a plurality of faultswhich can result from the assembling of the engine, and wherein thejudging step comprises identifying at least one of the plurality offaults, based on at least one of (a) an amount of deviation of themeasured timing of the at least one predetermined condition from areference timing and (b) a combination of at least two predeterminedconditions whose measured timings are deviated from at least tworeference timings, respectively.

[0018] According to another feature of the first aspect of theinvention, the testing method further comprising the step of deciding,when a measured timing of each of at least two predetermined conditionsof the pressure is equal to a reference timing, that there is no faultwith the assembling of the engine, and omitting carrying out the judgingstep. In this case, the judging step is prevented from being carried outuselessly.

[0019] According to another feature of the first aspect of theinvention, the plurality of timings comprise at least one timing whichcorresponds to each of at least two faults of the plurality of faults,and wherein the identifying step comprises utilizing one of theplurality of timings which corresponds to a smallest number of faults,prior to the other timings. In the case where a plurality of faults cansimultaneously occur to a single engine, the present testing method caneasily identify at least one fault out of the plurality of faults. Ifthe measured timing of occurrence of a certain predetermined conditionis judged as being different from the reference timing by, e.g., beingcompared with one of the plurality of timings which corresponds to thesmallest number of faults (e.g., one), the smallest number of faults canbe identified easily. The thus identified fault or faults can beutilized for identifying another or other remaining fault or faults.

[0020] According to another feature of the first aspect of theinvention, the identifying step comprises utilizing one of the pluralityof timings which corresponds to at least one fault the identification ofwhich is most easily confirmed by an an operator, prior to the othertimings. If the correctness of identification of at least one fault canbe confirmed by an operator, then it can be utilized for identifyinganother or other remaining fault or faults. The easier the confirmationis, the easier the employment of this identifying manner is.

[0021] According to another feature of the first aspect of theinvention, the identifying step comprises utilizing one of the pluralityof timings which corresponds to at least one fault which is most easilycorrected by an operator, prior to the other timings. In the case wherea plurality of faults occur to a single engine, if at least one faultout of the plurality of faults is identified and corrected, one or moreremaining faults can be identified more easily, or one or more faultswhich have been judged as being not identifiable turn to beidentifiable.

[0022] According to another feature of the first aspect of theinvention, the rotating step comprises rotating, using an independentrotating device, a crank shaft of the assembled engine and therebyreciprocating a piston of the engine in a cylinder of the engine, whilethe at least one of the intake-valve side and exhaust-valve side spacesis isolated from an atmosphere, and wherein the judging step comprisesjudging whether there is at least one fault with an assembled state ofthe engine, based on at least one of (a) a pressure in the one of theintake-valve side and exhaust-valve side spaces which is measured whilea corresponding one of the intake and exhaust valves is closed and (b)at least one of a starting and an ending timing of a closed state of oneof the intake and exhaust valves which corresponds to the one of theintake-valve side and exhaust-valve side spaces.

[0023] According to another feature of the first aspect of theinvention, the rotating step comprises rotating, using an independentrotating device, a crank shaft of the assembled engine and therebyreciprocating a piston of the engine in a cylinder of the engine, whilethe at least one of the intake-valve side and exhaust-valve side spacesis isolated from an atmosphere, and wherein the judging step comprisesjudging whether there is at least one fault with an assembled state ofthe engine, based on at least one of (a) a pressure in the one of theintake-valve side and exhaust-valve side spaces which is measured whilea corresponding one of the intake and exhaust valves is closed and (b)at least one of a starting and an ending timing of a closed state of oneof the intake and exhaust valves which corresponds to the one of theintake-valve side and exhaust-valve side spaces.

[0024] According to another feature of the first aspect of theinvention, the assembled engine includes a plurality of cylinders eachof which has an intake valve and an exhaust valve, wherein the measuringstep comprises measuring, for each of at least two cylinders of theplurality of cylinders, at least one of (a) a value of a pressure in atleast one of an external intake-valve side space which communicates withthe intake valve corresponding to the each cylinder and an externalexhaust-valve side space which communicates with the exhaust valvecorresponding to the each cylinder, when the pressure satisfies the atleast one predetermined condition, and (b) a timing at which thepressure satisfies the at least one predetermined condition, wherein themethod further comprises a step of comparing the at least one of thevalue and the timing of a first one of the at least two cylinders withthe at least one of the value and the timing of a second one of the atleast two cylinders, and wherein the judging step comprises judging thatthere is at least one fault with the assembling of the engine, when theat least one of the value and the timing of the first cylinder is notequal to the at least one of the value and the timing of the secondcylinder.

[0025] According to a second aspect of the present invention, there isprovided a method of testing an engine including a cylinder, a piston, acrank shaft, an intake valve and an exhaust valve, characterized byrotating, using an independent rotating device, the crank shaft andthereby reciprocating the piston in the cylinder, while at least one ofan external intake-valve side space which communicates with the intakevalve and an external exhaust-valve side space which communicates withthe exhaust valve is isolated from an atmosphere, and evaluating a stateof the engine based on at least one of (a) a pressure in the one of theintake-valve side and exhaust-valve side spaces which is measured whilea corresponding one of the intake and exhaust valves is closed and (b)at least one of a starting and an ending timing of a closed state of oneof the intake and exhaust valves which corresponds to the one of theintake-valve side and exhaust-valve side spaces.

[0026] The engine testing method in accordance with the second aspect ofthe invention may be carried out on an engine which is provided with anignition plug. In this case, the method can be carried out withouthaving to remove the ignition plug from the engine. If the method isperformed with the intake and exhaust valves being closed, the innerspace of the cylinder is isolated from not only the intake-valve sideand exhaust-valve side spaces but the atmosphere. In the case where themethod is performed with the intake-valve side space being isolated fromthe atmosphere, the intake-valve side space is completely isolated ifthe intake valve or valves is or are completely closed, so that thepressure in the intake-valve side space becomes constant irrespective ofthe reciprocation of the piston. Similarly, in the case where the methodis performed with the exhaust-valve side space being isolated from theatmosphere, the exhaust-valve side space is completely isolated if theexhaust valve or valves is or are completely closed, so that thepressure in the exhaust-valve side space becomes constant irrespectiveof the reciprocation of the piston. Since it is easy to detect theconstant-pressure state of the intake-valve side or exhaust-valve sidespace, it is also easy to find one or more faults with the engine basedon the detection result. For example, it is easy to find the fault ofincomplete valve closing, that is, the fault that an intake or exhaustvalve does not completely close because, e.g., a foreign matter bitesinto the space between the intake or exhaust valve and a correspondingvalve seat. If the incomplete valve closing or the foreign-matter bitingoccurs, the pressure of the intake-valve side space (“the intakepressure”) or the pressure of the exhaust-valve side space (“the exhaustpressure”) which would be constant if the engine would be normal changesas the pressure of the inner space of the cylinder (“the cylinderpressure”) changes with the rotation of the crank shaft. Therefore, if achange of the intake or exhaust pressure is detected at a timing whenthe intake or exhaust pressure should be constant, it can be judged thatthe engine being tested has the fault of incomplete valve closing. Inaddition, since it is easy to detect the constant state of the intake orexhaust pressure, it is also easy to detect the starting and endingtimings of the constant state of the intake or exhaust pressure. Sincethe starting and ending timings correspond to the opening and closingtimings of the intake or exhaust valve, it is easy to determine theopening and closing timings, indirectly based on the starting and endingtimings. However, the opening and closing timings of the intake orexhaust valve may be determined directly by using an exclusivevalve-position sensor or sensors. Moreover, the intake or exhaustpressure is naturally raised when the piston reciprocates in thecylinder and the pressurized air in the inner space of the cylinder issupplied to the intake-valve side or exhaust-valve side space. Thus, thepresent method does not need an exclusive pressure source for changingthe intake or exhaust pressure. The present method may be carried out onan engine just after the engine has been assembled from various parts ina factory, or when the engine is overhauled after some use.

[0027] According to a first preferred feature of the second aspect ofthe invention, the one of the intake-valve and exhaust-valve side spacescomprises the exhaust-valve side space, and the evaluating stepcomprises evaluating the state of the engine based on the pressure inthe exhaust-valve side space which is measured while the exhaust valveshould have been closed.

[0028] According to a second preferred feature of the second aspect ofthe invention, the evaluating step comprises judging that the exhaustvalve has incompletely been closed, when the pressure in theexhaust-valve side space changes while the exhaust valve should havebeen closed.

[0029] According to a third preferred feature of the second aspect ofthe invention, the judging step comprises judging that the exhaust valvehas incompletely been closed, when the pressure in the exhaust-valveside space measured while the exhaust valve should have been closed ishigher than a first reference value.

[0030] According to a fourth preferred feature of the second aspect ofthe invention, or according to any one of the above-indicated first tothird preferred features, the one of the intake-valve and exhaust-valveside spaces comprises the exhaust-valve side space, and the evaluatingstep comprises judging that the intake valve has incompletely beenclosed, when the pressure in the exhaust-valve side space measured whilethe exhaust valve is open is lower than a second reference value. In thecase where the exhaust pressure is measured in the manner in which theexhaust-valve side space is isolated from the atmosphere and theintake-valve side space is communicated with the atmosphere, both thecylinder pressure and the exhaust pressure are raised as the piston ismoved up with the exhaust valve being opened and the intake valve beingclosed, because air is compressed in both the inner space of thecylinder and the exhaust-valve side space. However, if the intake valvehas not completely closed, the air in the inner space of the cylinderpartly flows into the atmosphere via the intake valve, so that theexhaust pressure takes a maximum value lower than that taken when theintake valve is normal. Thus, the present method can identify the faultof incomplete intake-valve closing.

[0031] According to a fifth preferred feature of the second aspect ofthe invention, or according to any one of the above-indicated first tofourth preferred features, the evaluating step comprises astate-change-timing depending evaluating step for evaluating the stateof the engine based on the at least one of the starting and endingtimings of the closed state of the one of the intake and exhaust valveswhich corresponds to the one of the intake-valve side and exhaust-valveside spaces which is isolated from the atmosphere, the at least one ofthe starting and ending timings of the closed state of the one valvecomprising at least one of a first state-change timing when the pressurein the one space changes from a changing state to a constant state and asecond state-change timing when the pressure in the one space changesfrom the constant state to the changing state.

[0032] According to a sixth preferred feature of the second aspect ofthe invention, the pressure-change-timing depending evaluating stepcomprises evaluating the state of the engine based on an intervalbetween the first and second state-change timings. The occurrence orpresence of one sort of fault may change or move both the first andsecond state-change timings in the same direction along the axis oftime, and the presence of another sort of fault may move the first andsecond state-change timings in the opposite directions. Therefore, oneor more faults may be identified based on the interval between the firstand second state-change timings. In addition, since this intervaldepends on all the faults that influence at least one of the first andsecond state-change timings, it is possible to identify, based on thesingle amount (i.e., the interval), a fault which influences both of thetwo timings.

[0033] According to a seventh preferred feature of the second aspect ofthe invention, or according to any one of the above-indicated first tosixth preferred features, the rotating step comprises anopposite-direction rotating step for rotating, using the independentrotating device, the crank shaft of the engine in an opposite directionopposite to a normal direction in which the crank shaft is rotated whenthe engine is actually operated by firing. In the case where the engineis rotated by the independent rotating device, the engine can be easilyrotated in the opposite direction, so that information can be obtainedwhich cannot be obtained when the engine is rotated in the normaldirection. Thus, one or more bad states of the engine which cannot beidentified based on only the information obtained when the engine isrotated in the normal direction, can be identified based on theinformation obtained when the engine is rotated in the oppositedirection. In addition, the reliability of evaluation of one or more badstates of the engine can be improved based on the information obtainedwhen the engine is rotated in the opposite direction. Theopposite-direction rotating step may be carried out independent of thefirst or second aspect of the invention. In the last case, too, the stepprovides the same advantages.

[0034] According to an eighth preferred feature of the second aspect ofthe invention, the opposite-direction rotating step comprises rotatingthe crank shaft of the engine in the opposite direction while theintake-valve side space is isolated from the atmosphere. Thisopposite-direction rotating step is symmetrical with thenormal-direction rotating step in which the exhaust-valve side space isisolated from the atmosphere and the engine is rotated in the normaldirection. Accordingly, for example, the order of opening of the intakeand exhaust valves is reversed. Thus, very important information can beobtained.

[0035] According to a ninth preferred feature of the second aspect ofthe invention, or according to any one of the above-indicated first toeighth preferred features, the rotating step comprises anormal-direction rotating step for rotating, using the independentrotating device, the crank shaft of the engine in a normal direction inwhich the crank shaft is rotated when the engine is actually operated byfiring.

[0036] According to a tenth preferred feature of the second aspect ofthe invention, the opposite-direction rotating step comprises rotatingthe crank shaft of the engine in the normal direction while theexhaust-valve side space is isolated from the atmosphere. In this enginetesting method, various sorts of useful information can be obtained, andone or more bad states of the engine can be identified based on theinformation.

[0037] According to an eleventh preferred feature of the second aspectof the invention, or according to any one of the above-indicated firstto tenth preferred features, the testing method further comprising thestep of isolating, using a valve which is selectively opened and closed,the at least one of the intake-valve side and exhaust-valve side spacesfrom the atmosphere. In this case, the intake-valve side and/orexhaust-valve side spaces are easily isolated from the atmosphere, byclosing one or more valves provided for the space or spaces. Therefore,the efficiency of the engine tests is improved.

[0038] According to a third aspect of the present invention, there isprovided a method of testing an assembled internal combustion engineincluding a plurality of cylinders each of which has an intake valve andan exhaust valve, characterized by rotating the assembled engine,measuring, for each of at least two cylinders of the plurality ofcylinders, at lest one of (a) a value of a pressure in at least one ofan external intake-valve side space which communicates with the intakevalve corresponding to the each cylinder and an external exhaust-valveside space which communicates with the exhaust valve corresponding tothe each cylinder, when the pressure satisfies a predeterminedcondition, and (b) a timing at which the pressure satisfies thepredetermined condition, comparing the at least one of the value and thetiming of a first one of the at least two cylinders with the at leastone of the value and the timing of a second one of the at least twocylinders, and judging that there is at least one fault with theassembling of the engine, when the at least one of the value and thetiming of the first cylinder is not equal to the at least one of thevalue and the timing of the second cylinder.

[0039] In the testing method in accordance with the third aspect of theinvention, the timing at which the pressure in the intake-valve sidespace or the external exhaust-valve side space (hereinafter, referred toas “the intake pressure” or the “exhaust pressure”) satisfies thepredetermined condition changes depending upon the changing pressure ina cylinder (hereinafter, referred to as the “cylinder pressure”) inwhich a piston reciprocates linearly and the opening and closing timingsof the intake and exhaust valves. The cylinder pressure increases as thepiston moves up toward its top dead position, and decreases as thepiston moves down toward its bottom dead position. In the reciprocatingengine, after the intake and exhaust valves close, first, the exhaustvalve starts opening and subsequently the intake valve starts opening.After the exhaust valve closes, the intake valve closes. During eachcycle, if, e.g., the timing of commencement of opening of the intakevalve is earlier (i.e., corresponds to a smaller CS angle) than areference timing obtained from a normal engine, the exhaust pressuretakes a maximal value smaller than a reference value obtained from thenormal engine and takes a less time to reach the maximal value. To thecontrary, if the timing of commencement of opening of the intake valveis later (i.e., corresponds to a larger CS angle) than the referencetiming obtained from the normal engine, the exhaust pressure takes amaximal value greater than the reference value and takes a more time toreach the maximal value. Therefore, if, e.g., the timing when theexhaust pressure takes a maximal value is known, the relationshipbetween the opening and closing timings of the intake valve and the CSangle is known. Thus, it can be judged that the assembled engine has theassembling fault of an incorrect phase difference between a crank shaftand a cam shaft. In addition, if, e.g., the opening and closing timingsof the exhaust valve change relative to the CS angle, the changeinfluences the intake pressure. Thus, the fault of incorrect phasedifference between the crank and cam shafts can be identified based onthe timing of occurrence of at least one predetermined condition of theintake pressure. In this way, it is possible to judge, without having totake the engine apart, whether there is at least one fault with theassembled engine, based on at least one of the value of the intakeand/or exhaust pressure when the pressure satisfies the predeterminedcondition, and the timing at which the pressure satisfies thepredetermined condition. In the present engine testing method, one ormore assembling faults of the engine is or are found by measuring, forat least two cylinders, at least one of a value of the pressure when thepressure satisfies the predetermined condition and a timing at which thepressure satisfies the predetermined condition, and comparing thepressure value and/or timing obtained for one cylinder with the pressurevalue and/or timing obtained for another or the other cylinder. Forexample, there are some cases where the pressure value obtained for anabnormal cylinder having an assembling fault is different from thatobtained for a normal cylinder. If the difference is detected, it can bejudged that one of those two or more cylinders has an assembling fault.If this comparison is made among more cylinders, more information aboutthe assembled state of the engine can be obtained. Thus, one or morecylinders having an assembling fault can be specified with higheraccuracy. Since in this method it is not necessary to determine CSangles corresponding to the pressure values and/or timings obtained forthe cylinders, an apparatus for carrying out the method can enjoy asimpler construction. As far as the present invention is concerned, theterm “comparing” encompasses judging whether there is a significantdifference between the combination of respective values of a pluralityof parameters obtained for one cylinder and that obtained for anothercylinder and, in the last case, the term “equal” means that all therespective values of the combination for the first cylinder are equal tothose of the combination for the second cylinder. The present methoddoes not exclude finding an assembling fault by comparing a value of theintake or exhaust pressure when the pressure satisfies the predeterminedcondition with respect to each cylinder, with a reference value obtainedfrom one or more normal engines. For example, the maximal value of theexhaust pressure obtained from each cylinder may be compared with areference maximal value obtained from normal engines. The assembledengine may be rotated in a “hot” state, i.e., by firing of fuel therein,or in a “cool” state, i.e., by being connected to a separate rotatingdevice and compulsorily rotated by the device. Generally, the “cool”test is easier than the “hot” test. In the hot test, it is cumbersome tosupply fuel to the engine and treat the exhaust gas emitted therefrom.In addition, in the “hot” test, the pressure signals obtained from theintake-side and exhaust-side spaces contain more noise. The “cool” testis free from those problems, and accordingly can be carried out moreeasily.

[0040] According to a first preferred feature of the third aspect of theinvention, the assembled engine includes a first bank having at leastone cylinder, and a second bank having at least one cylinder, whereinthe comparing step comprises comparing the at least one of the value andthe timing of the at least one cylinder of the first bank with the atleast one of the value and the timing of the at least one cylinder ofthe second bank. For example, if a fault occurs to the phase of the camshaft of one of two banks of a V-type engine, the pressure value and/ortiming obtained for a cylinder of the one bank corresponding to the camshaft having the fault is different from the pressure value and/ortiming obtained for a cylinder of the other bank corresponding to thecam shaft having no fault. The present method can find at least onefault which can occur to each one of the two banks independent of theother bank.

[0041] According to a second preferred feature of the third aspect ofthe invention, or the above-indicated first preferred feature, thecomparing step comprises comparing the at least one of the value and thetiming of each of the at least two cylinders with at least one of anaverage of the respective values of the at least two cylinders and anaverage of the respective timings of the at least two cylinders. Thepressure value or the timing obtained for each cylinder may change byvarious amounts, including a very small or large one, corresponding tovarious sorts of assembling faults. Those changes may include not onlychanges corresponding to faults but also changes resulting frommeasurement errors. It is preferable to remove the latter changes. Thepresent engine testing method can reduce the influences of the latterchanges, thereby finding at least one fault with improved accuracy.

[0042] According to a third preferred feature of the third aspect of theinvention, or the above-indicated first or second preferred feature, thecomparing step comprises dividing the at least two cylinders into atleast two groups including a first group including at least one cylinderand a second group including at least one cylinder the at least one ofthe value and the timing of which significantly differs from the atleast one of the value and the tiring of the at least one cylinder ofthe first group, and comparing the at least one of the value and thetiming of the at least one cylinder of the first group with the at leastone of the value and the timing of the at least one cylinder of thesecond group. The present engine testing method enjoys the sameadvantage as that of the method according to the second preferredfeature of the invention.

[0043] According to a fourth preferred feature of the third aspect ofthe invention, or any of the above-indicated first to third preferredfeatures, the measuring step comprises measuring, for every one of theplurality of cylinders, a timing at which the pressure satisfies thepredetermined condition, and the comparing step comprises comparing atime interval between respective times when the respective pressures ofa first pair of successively firing cylinders of the plurality ofcylinders satisfy the predetermined condition, with a time intervalbetween respective times when the respective pressures of a second pairof successively firing cylinders of the plurality of cylinders satisfythe predetermined condition. As will be described in connection with thepreferred embodiments of the invention, one or more faults which occurat a very high frequency can be easily detected by the simple method inwhich a time interval between respective times when the respectivepressures of a first pair of successively firing cylinders satisfy thepredetermined condition, with a time interval between respective timeswhen the respective pressures of a second pair of successively firingcylinders satisfy the predetermined condition. Those faults includefaults with the respective clearances of the intake and exhaust valves.In the case where the engine being tested includes two banks, thosefaults additionally include faults with the respective cam pulleys andrespective driven gears of the two banks.

[0044] According to a fifth preferred feature of the third aspect of theinvention, or any of the above-indicated first to fourth preferredfeatures, the measuring step comprises measuring, for every one of theplurality of cylinders, at least one of (a) a value of the pressure whenthe pressure satisfies the predetermined condition and (b) a timing atwhich the pressure satisfies the predetermined condition.

[0045] According to a sixth preferred feature of the third aspect of theinvention, or any of the above-indicated first to fifth preferredfeatures, the comparing step comprises dividing the at least twocylinders into at least two groups including a first group including atleast two cylinders and a second group including at least two cylindersthe at least one of the value and the timing of each one of whichsignificantly approximates to the at least one of the value and thetiming of the other or another cylinder of the at least two cylinders ofthe second group and significantly differs from the at least one of thevalue and the timing of each of the at least two cylinders of the firstgroup, and comparing the at least one of the value and the timing ofeach of the at least two cylinders of each of the first and secondgroups with the at least one of the value and the timing of the other oranother cylinder of the at least two cylinders of the each group.

[0046] According to a seventh preferred feature of the third aspect ofthe invention, or any of the above-indicated first to sixth preferredfeatures, the measuring step comprises measuring, for every one of theplurality of cylinders, a value of the pressure when the pressuresatisfies the predetermined condition, and the comparing step comprisescomparing the respective values of every pair of successively firingcylinders of the plurality of cylinders, with each other.

[0047] According to an eighth preferred feature of the third aspect ofthe invention, or any of the above-indicated first to seventh preferredfeatures, the predetermined condition comprises at least one of a firstcondition that the exhaust pressure in the exhaust-valve side spacetakes a maximal value; a second condition that the exhaust pressure isin a constant state in which the exhaust pressure takes a constant valueas timing elapses; a third condition that the exhaust pressure changesfrom the constant state to a decreasing state; a fourth condition thatthe intake pressure in the intake-valve side space takes a maximalvalue; and a fifth condition that the intake pressure changes from aconstant state in which the intake pressure takes a constant value astiming elapses, to an increasing state.

[0048] According to a ninth preferred feature of the third aspect of theinvention, the value of the pressure when the pressure satisfies thepredetermined condition comprises at least one of the maximal value andthe constant value.

[0049] According to a tenth preferred feature of the third aspect of theinvention, or the above-indicated eighth preferred feature, the timingat which the pressure satisfies the predetermined condition comprises atleast one of a timing at which the first condition occurs; a timing atwhich the second condition starts; a timing at which the third conditionoccurs; a timing at which the fourth condition occurs; a timing at whichthe fifth condition occurs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The above and optional objects, features, and advantages of thepresent invention will be better understood by reading the followingdetailed description of the preferred embodiments of the invention whenconsidered in conjunction with the accompanying drawings, in which

[0051]FIG. 1 is a perspective view of a pertinent portion of an internalconstruction of a V6 gasoline engine which is tested by an enginetesting method as a first embodiment of the present invention;

[0052]FIG. 2 is a perspective view of the V6 engine of FIG. 1 which hasfaults with a crank pulley and a cam pulley;

[0053]FIG. 3 is an enlarged cross-section view of a part of a dynamicvalve system of the V6 engine of FIG. 1;

[0054]FIG. 4 is a diagrammatic view of an essential portion of an enginetesting apparatus which carries out the engine testing method as thefirst embodiment of the invention;

[0055]FIG. 5 is a front elevation view of the engine testing apparatusof FIG. 4;

[0056]FIG. 6 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of position, PP, of the piston,and the respective changes of the exhaust and intake pressures, P_(EX),P_(IN), of a cylinder of a normal engine, and the phase or angle,Θ_(crank), of a crank shaft of the engine;

[0057]FIG. 7 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of a crank-shaft referencesignal obtained from the crank shaft of the normal engine and therespective changes of exhaust pressures P_(EX) obtained from all thecylinders of the engine, and the crank-shaft angle Θ_(crank);

[0058]FIG. 8 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of an exhaust pressure P_(EX)obtained from the normal engine and the change of an exhaust pressureP_(EX) obtained from an engine having the fault of small intake-valveclearance, and the crank-shaft angle Θ_(crank);

[0059]FIG. 9 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of an exhaust pressure P_(EX)obtained from the normal engine and the change of an exhaust pressureP_(EX) obtained from an engine having the fault of large intake-valveclearance, and the crank-shaft angle Θ_(crank);

[0060]FIG. 10 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of an intake pressure P_(IN)obtained from the normal engine, the change of an intake pressure P_(IN)obtained from an engine having the fault of small intake-valveclearance, and the change of an intake pressure P_(IN) obtained from anengine having the fault of large intake-valve clearance, and thecrank-shaft angle crank;

[0061]FIG. 11 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of an exhaust pressure P_(EX)obtained from the normal engine and the change of an exhaust pressureP_(EX) obtained from an engine having the fault of small exhaust-valveclearance, and the crank-shaft angle Θ_(crank);

[0062]FIG. 12 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of an exhaust pressure P_(EX)obtained from the normal engine and the change of an exhaust pressureP_(EX) obtained from an engine having the fault of large exhaust-valveclearance, and the crank-shaft angle Θ_(crank);

[0063]FIG. 13 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of an exhaust pressure P_(EX)obtained from the normal engine and the change of an exhaust pressureP_(EX) obtained from an engine having the fault of compression-ringmissing, and the crank-shaft angle Θ_(crank);

[0064]FIG. 14 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of crank-shaft reference signalobtained from the normal crank shaft of an engine and the respectivechanges of exhaust pressures P_(EX) obtained from all the cylinders ofthe engine having the fault of cam-pulley one-tooth fast state, and thecrank-shaft angle Θ_(crank);

[0065]FIG. 15 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of crank-shaft reference signalobtained from the normal crank shaft of an engine and the respectivechanges of exhaust pressures P_(EX) obtained from all the cylinders ofthe engine having the fault of cam-pulley one-tooth slow state, and thecrank-shaft angle Θ_(crank);

[0066]FIG. 16 is a graph showing the relationship, obtained by theapparatus of FIG. 4, between the change of crank-shaft reference signalobtained from the normal crank shaft of an engine, the change of intakepressure P_(IN) obtained from the normal engine, the change of intakepressure P_(IN) obtained from an engine having the fault ofright-cam-pulley one-tooth fast state, the change of intake pressureP_(IN) obtained from an engine having the fault of right-cam-pulleyone-tooth slow state, the change of intake pressure P_(IN) obtained froman engine having the fault of crank-pulley one-tooth fast state, and thechange of intake pressure P_(IN) obtained from an engine having thefault of crank-pulley one-tooth slow state, and the crank-shaft angleΘ_(crank);

[0067]FIG. 17 is a graph showing the change of exhaust pressure P_(EX)obtained from the normal engine and the change of exhaust pressureP_(EX) obtained from an engine having the fault of crank-pulleyone-tooth slow state or cam-pulley one-tooth fast state, with respect tothe crank-shaft angle Θ_(crank);

[0068]FIG. 18 is a graph showing the change of exhaust pressure P_(EX)obtained from the normal engine and the change of exhaust pressureP_(EX) obtained from an engine having the fault of crank-pulleyone-tooth fast state or cam-pulley one-tooth slow state, with respect tothe crank-shaft angle Θ_(crank);

[0069]FIG. 19 is a graph showing the change of crank-shaft referencesignal obtained from the normal crank shaft of an engine and therespective changes of exhaust pressures P_(EX) obtained from all thecylinders of the engine having the fault of driven-gear one-tooth faststate, with respect to the crank-shaft angle Θ_(crank);

[0070]FIG. 20 is a graph showing the change of crank-shaft referencesignal obtained from the normal crank shaft of an engine and therespective changes of exhaust pressures P_(EX) obtained from all thecylinders of the engine having the fault of driven-gear one-tooth slowstate, with respect to the crank-shaft angle Θ_(crank);

[0071]FIG. 21 is a graph showing the change of crank-shaft referencesignal obtained from the normal crank shaft of an engine, the change ofintake pressure P_(IN) obtained from the normal engine, the change ofintake pressure P_(IN) obtained from an engine having the fault ofright-driven-gear one-tooth fast state, and the change of intakepressure P_(IN) obtained from an engine having the fault ofright-driven-gear one-tooth slow state, with respect to the crank-shaftangle Θ_(crank);

[0072]FIG. 22 is a graph showing the change of exhaust pressure P_(EX)obtained from the normal engine and the change of exhaust pressureP_(EX) obtained from an engine having the fault of driven-gear one-toothfast state, with respect to the crank-shaft angle Θ_(crank);

[0073]FIG. 23 is a graph showing the change of exhaust pressure P_(EX)obtained from the normal engine and the change of exhaust pressureP_(EX) obtained from an engine having the fault of driven-gear one-toothslow state, with respect to the crank-shaft angle Θ_(crank);

[0074]FIG. 24 is a table showing respective actual values of anexhaust-pressure maximal-value difference, α, an exhaust-pressureconstant-value difference, β, an exhaust-pressure maximal-value-angledifference, Γ, an exhaust-pressure constant-start-angle difference, Σ,an exhaust-pressure decrease-start-angle difference, Φ, anintake-pressure maximal-value-angle difference, Λ, and anintake-pressure increase-start-angle difference, Ψ, which are obtainedin the case where each one of assembling faults occurs independent ofthe other faults;

[0075]FIG. 25 is a flow chart representing the main routine of an enginetesting program which is pre-stored in a ROM (read only memory) of afault finder of the apparatus of FIG. 4;

[0076]FIG. 26 is a front elevation view of a display device of theapparatus of FIG. 4;

[0077]FIG. 27 is a flow chart representing a fault specifying routinecarried out at Step S118 of the flow chart of FIG. 25;

[0078]FIG. 28 is a view illustrating the respective bits of each ofeight fault flags which are provided in a RAM (random access memory) ofthe fault finder of the apparatus of FIG. 4;

[0079]FIG. 29 is a flow chart representing a crank-pulley test routinecarried out at Step S202 of the flow chart of FIG. 27;

[0080]FIG. 30 is a flow chart representing a cam-pulley and driven-geartest 1 routine carried out at Step S206 of the flow chart of FIG. 27;

[0081]FIG. 31 is a flow chart representing a cam-pulley and driven-geartest 2 routine carried out at Step S210 of the flow chart of FIG. 27;

[0082]FIG. 32 is a flow chart representing a valve-clearance andcompression-ring test routine carried out at Step S214 of the flow chartof FIG. 27;

[0083]FIG. 33 is a flow chart representing another fault specifyingroutine which is carried out at Step S118 of the flow chart of FIG. 25,in place of the routine represented by the flow chart of FIG. 27, inanother engine testing method as a second embodiment of the invention;

[0084]FIG. 34 is a flow chart representing a test 1 routine carried outat Step S700 of the flow chart of FIG. 33;

[0085]FIG. 35 is a flow chart representing a test 2 routine carried outat Step S702 of the flow chart of FIG. 33;

[0086]FIG. 36 is a flow chart representing a test 2-1 routine carriedout at Step S908 of the flow chart of FIG. 35;

[0087]FIG. 37 is a flow chart representing a test 2-2 routine carriedout at Step S910 of the flow chart of FIG. 35;

[0088]FIG. 38 is a flow chart representing a test 2-3 routine carriedout at Step S916 of the flow chart of FIG. 35;

[0089]FIG. 39 is a flow chart representing a test 3 routine carried outat Step S704 of the flow chart of FIG. 33;

[0090]FIG. 40 is a graph showing the ranges of the exhaust-pressuredecrease-start-angle difference (employed at Step S802 of the flow chartof FIG. 34;

[0091]FIG. 41 is a graph showing the ranges of the exhaust-pressuremaximal-value-angle difference Γ employed at Step S904 of the flow chartof FIG. 35;

[0092]FIG. 42 is a diagrammatic view corresponding to FIG. 4, andshowing an essential portion of another engine testing apparatus whichcarries out another engine testing method as a third embodiment of theinvention;

[0093]FIG. 43 is a graph showing the relationship, obtained by theapparatus of FIG. 42, between the change of crank-shaft reference signalobtained from the normal crank shaft of an engine, the respectivechanges of exhaust pressures P_(EX) obtained from the right and leftbanks of an normal engine, the respective changes of exhaust pressuresP_(EX) obtained from the right and left banks of an engine having thefault of left-cam-pulley one-tooth fast state, and the respectivechanges of exhaust pressures P_(EX) obtained from the right and leftbanks of an engine having the fault of left-cam-pulley one-tooth slowstate, and the crank-shaft angle Θ_(crank);

[0094]FIG. 44 is a graph showing the relationship, obtained by theapparatus of FIG. 42, between the change of exhaust pressure P_(EX)obtained from the left bank of the normal engine, the change of exhaustpressure P_(EX) obtained from the left bank of the engine having thefault of left-driven-gear one-tooth fast state, and the change ofexhaust pressure P_(EX) obtained from the left bank of the engine havingthe fault of left-driven-gear one-tooth slow state, and the crank-shaftangle Θ_(crank);

[0095]FIG. 45 is a graph showing the relationship, obtained by theapparatus of FIG. 42, between the change of crank-shaft reference signalobtained from the normal crank shaft of an engine, the respectivechanges of exhaust pressures P_(EX) obtained from the right and leftbanks of an normal engine, the respective changes of exhaust pressuresP_(EX) obtained from the right and left banks of an engine having thefault of left-driven-gear one-tooth fast state, and the respectivechanges of exhaust pressures P_(EX) obtained from the right and leftbanks of an engine having the fault of left-driven-gear one-tooth slowstate, and the crank-shaft angle Θ_(crank);

[0096]FIG. 46 is a graph showing the relationship, obtained by theapparatus of FIG. 42, between the change of exhaust pressure P_(EX)obtained from the left bank of the normal engine, the change of exhaustpressure P_(EX) obtained from the left bank of the engine having thefault of left-driven-gear one-tooth fast state, and the change ofexhaust pressure P_(EX) obtained from the left bank of the engine havingthe fault of left-driven-gear one-tooth slow state, and the crank-shaftangle Θ_(crank);

[0097]FIG. 47 is a table showing respective actual values of anexhaust-pressure maximal-value-angle difference Γ, an exhaust-pressureconstant-start-angle difference Σ, an exhaust-pressure maximal-valuedifference α, and an exhaust-pressure constant-value difference β, whichare obtained in the case where each one of the cam-pulley one-tooth fastand slow states and the driven-gear one-tooth fast and slow statesoccurs independent of the other faults;

[0098]FIG. 48 is a graph showing the change of an exhaust pressureP_(EX) obtained from a normal engine with respect to the crank-shaftangle, and the change of an exhaust pressure P_(EX) obtained from anengine having the exhaust-valve foreign-matter biting, both of which areutilized in another engine testing method as a fourth embodiment of theinvention;

[0099]FIG. 49 is a graph showing the change of an exhaust pressureP_(EX) obtained from a normal engine with respect to the crank-shaftangle, and the change of an exhaust pressure P_(EX) obtained from anengine having the intake-valve foreign-matter biting;

[0100]FIG. 50 is a table showing respective actual values of anexhaust-pressure maximal-value difference α, an exhaust-pressureconstant-value difference β, an exhaust-pressure maximal-value-angledifference Γ, an exhaust-pressure constant-start-angle difference Σ, anexhaust-pressure decrease-start-angle difference Φ, an intake-pressuremaximal-value-angle difference Λ, and an intake-pressureincrease-start-angle difference Ψ which are obtained in the case whereeach one of faults including the intake-valve or exhaust-valveforeign-matter biting occurs independent of the other faults;

[0101]FIG. 51 is a flow chart representing the main routine of an enginetesting program which is pre-stored in a ROM of a fault finder of anengine testing apparatus which carries out the engine testing method asthe fourth embodiment;

[0102]FIG. 52 is a front elevation view of a display device of thetesting apparatus;

[0103]FIG. 53 is a flow chart representing a fault specifying routinecalled at Step T106 of the flow chart of FIG. 52;

[0104]FIG. 54 is a view illustrating the respective bits of each of tenfault flags which are provided in a RAM of the fault finder of thetesting apparatus;

[0105]FIG. 55 is a flow chart representing a crank-pulley test routinecalled at Step T202 of the flow chart of FIG. 53;

[0106]FIG. 56 is a flow chart representing a cam-pulley test routinecalled at Step T206 of the flow chart of FIG. 53;

[0107]FIG. 57 is a flow chart representing a driven-gear test routinecalled at Step T210 of the flow chart of FIG. 53;

[0108]FIG. 58 is a flow chart representing a foreign-matter-biting testroutine called at Step T214 of the flow chart of FIG. 53;

[0109]FIG. 59 is a flow chart representing a valve-clearance testroutine called at Step S218 of the flow chart of FIG. 53;

[0110]FIG. 60 is a flow chart representing a compression-ring testroutine called at Step S222 of the flow chart of FIG. 53;

[0111]FIG. 61 is a diagrammatic view corresponding to FIG. 4, andshowing an essential portion of another engine testing apparatus whichcarries out another engine testing method as a fifth embodiment of theinvention;

[0112]FIG. 62 is a graph showing the change of position PP of a pistonof a normal engine with respect to the crank-shaft angle Θ_(crank), andthe change of an intake pressure P_(IN) of the engine, both of which areobtained when the engine is rotated in a direction opposite to itsnormal direction;

[0113]FIG. 63 is a flow chart representing the main routine of an enginetesting program which is pre-stored in a ROM of a fault finder of anengine testing apparatus which carries out the engine testing method asthe fifth embodiment;

[0114]FIG. 64 is a flow chart representing a foreign-matter-biting testroutine called at Step T1008 of the flow chart of FIG. 63;

[0115]FIG. 65 is a graph showing an exhaust-pressure maximal-value-anglerelative difference, ΔΓ_(i), an exhaust-pressure constant-start-anglerelative difference, ΔΣ_(i), and an exhaust-pressuredecrease-start-angle relative difference, ΔΦ_(i), of each of cylindersof an engine having the one-tooth fast state of a right cam pulley,which is utilized by another engine testing method as a sixth embodimentof the invention;

[0116]FIG. 66 is a view illustrating the six values of relativedifference ΔΓ_(i) obtained from an engine having the one-tooth faststate of a right cam pulley;

[0117]FIG. 67 is a flow chart representing the main routine of an enginetesting program which is pre-stored in a ROM of a fault finder of anengine testing apparatus which carries out the engine testing method asthe sixth embodiment;

[0118]FIG. 68 is a flow chart representing a fault specifying routinecarried out at Step U118 of the flow chart of FIG. 67;

[0119]FIG. 69 is a view illustrating the respective bits of each ofeight fault flags which are provided in a RAM of the fault finder of thetesting apparatus;

[0120]FIG. 70 is a flow chart representing a one-tooth-fast-driven-geartest routine carried out at Step U202 of the flow chart of FIG. 68;

[0121]FIG. 71 is a flow chart representing asmall-exhaust-valve-clearance test routine carried out at Step U204 ofthe flow chart of FIG. 68;

[0122]FIG. 72 is a flow chart representing a cam-pulley test routinecarried out at Step U206 of the flow chart of FIG. 68;

[0123]FIG. 73 is a flow chart representing a one-tooth-slow-driven-gearand intake-valve-clearance test routine carried out at Step U208 of theflow chart of FIG. 68;

[0124]FIG. 74 is a graph showing the ranges of parameter, λ_(i)-ΔΓ_(m),which is employed at Step U602 of the flow chart of FIG. 73;

[0125]FIG. 75 is a flow chart representing alarge-exhaust-valve-clearance test routine carried out at Step U210 ofthe flow chart of FIG. 68;

[0126]FIG. 76 is a flow chart representing anotherlarge-exhaust-valve-clearance test routine carried out at Step U210 ofthe flow chart of FIG. 68;

[0127]FIG. 77 is a flow chart representing yet anotherlarge-exhaust-valve-clearance test routine carried out at Step U210 ofthe flow chart of FIG. 68;

[0128]FIG. 78 is a flow chart representing a compression-ring testroutine carried out at Step U212 of the flow chart of FIG. 68;

[0129]FIG. 79 is a table showing respective actual values of anexhaust-pressure maximal-value finite difference, δ_(PEXmax), anexhaust-pressure constant-value infinite difference, δ_(PEXconst), anexhaust-pressure maximal-value-angle infinite relative difference, δΓ,an exhaust-pressure constant-start-angle infinite relative difference,δΣ, an exhaust-pressure decrease-start-angle infinite relativedifference, δΦ, an intake-pressure maximal-value-angle infinite relativedifference, δΛ, and an intake-pressure increase-start-angle infiniterelative difference, δΨ, which are obtained in the case where each oneof the faults with the cam pulleys and the driven gears occursindependent of the other faults;

[0130]FIG. 80 is a table showing respective actual values ofexhaust-pressure maximal-value finite difference δ_(PEXmax),exhaust-pressure constant-value infinite difference δ_(PEXconst),exhaust-pressure maximal-value-angle infinite relative difference δθ,exhaust-pressure constant-start-angle infinite relative difference δΣ,exhaust-pressure decrease-start-angle infinite relative difference δΦ,intake-pressure maximal-value-angle infinite relative difference δΛ, andintake-pressure increase-start-angle infinite relative difference δΨwhich are obtained in the case where each one of the faults with theintake-valve clearance, the exhaust-valve clearance, and the compressionring occurs independent of the other faults; and

[0131]FIG. 81 is a flow chart representing an engine testing programwhich is pre-stored in a ROM of a fault finder of an engine testingapparatus which carries out the engine testing method as the seventhembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

[0132] There will be described an assembled engine testing method inaccordance with the present invention, together with an assembled enginetesting apparatus which is preferably employed for carrying out thetesting method.

[0133]FIG. 1 is a perspective view of a pertinent portion of a V-type6-cylinder DOHC (double over head cam) gasoline engine as an internalcombustion engine. The engine includes pistons 10, 12 each of whichreciprocates in a corresponding cylinder (not shown). The piston 10represents three pistons of the left bank (i.e., first bank) of the V6engine, and the piston 12 represents three pistons of the right bank(i.e., second bank) of the same. The reciprocation of each piston 10, 12is converted into rotation of a crank shaft 18 via a correspondingconnecting rod 14, and the rotation of the crank shaft 18 is output asthe power of the engine. The engine has a dynamic valve system 52including exhaust valves 48 and intake valves 50 each of which isoperated in synchronism with the rotation of the crank shaft 18.

[0134] The V6 engine has a cam shaft rotating mechanism 44 including acrank pulley 20 fixed to the crank shaft 18, a timing (cog) belt 22, aleft and a right cam pulley 24, 26, two exhaust cam shafts 28, 30 towhich the two cam pulleys 24, 26 are fixed, respectively, two intake camshafts 32, 34, two drive gears 36, 38 fixed to the two exhaust camshafts 28, 30, respectively, and two driven gears 40, 42 fixed to thetwo intake cam shafts 32, 34, respectively. The dynamic valve system 52includes a plurality of cams 46 provided on each of the cam shafts 28,30, 32, 34. When the cam shafts are rotated, those cams 46 open andclose the corresponding exhaust and intake valves 48, 50, respectively.

[0135] When the crank shaft 18 is rotated, the exhaust and intake valves48, 50 are operated via the crank pulley 20, the timing belt 22, the campulleys 24, 26, the cam shafts 28, 30, 32, 34, and the cams 46.Therefore, if the timing belt 22 loosens, the opening and closingtimings of each valve 48, 50 will change. This problem is prevented bythe provision of a belt idler 54 including an auto-tensioner (not shown)and additional belt idlers 56, 58 which do not include anyauto-tensioners. Those belt idlers 54, 56, 58 are effective inincreasing the number of meshed teeth of each of the timing belt 22, thecrank pulley 20, and the cam pulleys 24, 26. The two driven gears 40, 42are associated with two “scissors” gears 60, 62, respectively, in such amanner that the two scissors gears 60, 62 are rotatable relative to thetwo intake cam shafts 32, 34, respectively. Each scissors gear 60, 62 isbiased by a spring member (not shown) in a direction in which thescissors gear 60, 62 is rotated relative to the corresponding drivengear 40, 42 and the corresponding intake cam shaft 32, 34. Thus, thebacklash between the drive and driven gears 36, 38, 40, 42 iseffectively prevented and the generation of noise from the engine iseffectively reduced.

[0136] The opening and closing timings of each of the exhaust and intakevalves 48, 50 should accurately correspond to particular angular phasesof the crank shaft 18, respectively. Since the V6 engine which is to betested in the present embodiment is a four-cycle gasoline engine, theratio of the number of teeth of the crank pulley 20 to that of each campulley 24, 26 is 1 to 2. More specifically, the number of teeth of thecrank pulley is 24, and that of each cam pulley is 48. The ratio of thenumber of teeth of each drive gear 36, 38 to that of each driven gear40, 42 is 1 to 1. The number of teeth of each gear is 40.

[0137] When the engine is assembled from a number of elements or parts,it is essentially required that the opening and closing timings of eachof the exhaust and intake valves 48, 50 accurately correspond topredetermined angular phases of the crank shaft 18, respectively. Tothis end, phase-adjusting marks, “.”, “--” and “-”, are provided on thecrank pulley 20, the cam pulleys 24, 26, and the timing belt 22, asillustrated in enlarged partial views of FIG. 1, and those parts 20, 22,24, 26 are assembled such that those marks are aligned with each other.The drive and driven gears 36, 38, 40, 42 are likewise meshed with eachother. However, if the phase adjusting step is not appropriatelyperformed, each valve 48, 50 cannot accurately open or close at thepredetermined angular phases of the crank shaft 18. For example, if, asillustrated in an enlarged partial view of FIG. 2, the crank pulley 20is “faster” by one tooth than the timing belt 22, the opening andclosing timings of each valve 48, 50 are “slower” by 15 degrees (=360(degrees)/24) in terms of the angular phase of the crank shaft 18 thanthe respective positions of the corresponding piston in thecorresponding cylinder (not shown).

[0138] In addition, if, as illustrated in another enlarged view of FIG.2, the left cam pulley 24 is faster by one tooth than the timing belt22, the opening and closing timings of each valve 48, 50 of the leftbank are faster by 7.5 degrees (=360 (degrees)/48) in terms of theangular phase of the left exhaust cam shaft 28 than the respectivepositions of the corresponding piston in the corresponding cylinder.Moreover, if, as illustrated in yet another enlarged view of FIG. 2, theright driven gear 42 is faster by one tooth than the drive gear 38, theopening and closing timings of each valve 48, 50 of the right bank arefaster by 9 degrees (=360 (degrees)/40) in terms of the angular phase ofthe right intake cam shaft 34 than the respective positions of thecorresponding piston in the corresponding cylinder. The crank pulley 20may be slower by one tooth than the timing belt 22, the left or rightcam pulley 24, 26 may be slower by one tooth than the timing belt 22,and the left or right driven gear 40, 42 may be slower by one tooth thanthe left or right drive gear 36, 38. In rare cases, the crank pulley 20may be faster or slower by more than one tooth than the timing belt 22,the left or right cam pulley 24, 26 may be faster or slower by more thanone tooth than the timing belt 22, and the left or right driven gear 40,42 may be faster or slower by more than one tooth than the left or rightdrive gear 36, 38. Though the principle of the present invention isapplicable to various cases where one element is faster or slower bymore than one tooth than another element, it is assumed in the followingdescription that one element is faster or slower by just one tooth thananother element, for the purpose of easier understanding of the presentinvention.

[0139] The crank shaft 18 and the crank pulley 20 are designed such thatthe two elements 18, 20 can be connected to each other with no angularerror relative to each other. Therefore, even if the crank pulley 20 maybe faster or slower than the timing belt 22, there is no angular errorbetween the two elements 20, 22. This is also the case with therelationship between each exhaust cam shaft 28, 30 and the correspondingcam pulley 24, 26, and the relationship between each intake cam shaft32, 34 and the corresponding driven gear 40, 42.

[0140] The engine cannot exhibit its prescribed performance unless theopening and closing timings of each of the exhaust and intake valves 48,50 accurately correspond to prescribed angular phases of the crank shaft18. Hence, the cam shaft rotating mechanism 44 is assembled using theabove-described phase-adjusting marks. In addition, it is essentiallyrequired that the opening and closing timings of each of the exhaustvalves 48 accurately correspond to prescribed angular phases of thecorresponding exhaust cam shaft 28, 30 of the dynamic valve system 52and the opening and closing timings of each of the intake valves 50accurately correspond to prescribed angular phases of the correspondingintake cam shaft 32, 34 of the same 52. To this end, a “clearance” ofeach valve 48, 50 must be accurate or correct. The clearance of eachvalve 48, 50 is defined as the maximum distance between a shim 72 fixedto a lifter 70 of the valve and the corresponding cam 46. This valveclearance is influenced by the thickness of the shim 72, or thethickness of a seat member 74 fixed to the cylinder head 76, as can beseen from FIG. 3. Therefore, if one or both of those parameters is orare incorrect, an incorrect valve clearance will result. If theclearance of each valve 48, 50 is too large, the opening timing of thevalve delays and the closing timing of the same advances; and on theother hand, if too small, vice versa, that is, the opening timing ofeach valve 48, 50 advances and the closing timing of the same delays.

[0141] There will be described the assembled engine testing apparatusfor finding the fast or slow state of the crank pulley 20, the fast orslow state of each cam pulley 24, 26, the fast or slow state of eachdriven gear 40, 42, the large or small clearance of each valve 48, 50,and the missing of a compression ring 144 (136, 138, FIG. 4).

[0142]FIG. 4 is a diagrammatic view of the engine testing apparatus. Aninternal combustion engine 90 (only the left bank thereof is shown forsimplification) which is to be tested by the testing apparatus includessix cylinder heads 76 of the left and right banks, two intake manifolds94, and a single surge tank 96. The two intake manifolds 94 are providedin the left and right banks, respectively, and each intake manifold 94communicates with respective intake ports 92 of the three cylinders (orthree cylinder heads 76) of the corresponding bank. The surge tank 96communicates with the two intake manifolds 94. The testing apparatusincludes a single first pressure sensor 98 common to all the cylinders,six cover members 102, six O rings 104, six second pressure sensors 106,a single first analog to digital (A/D) converter 110, and six second A/Dconverters 112, a crank-shaft angle sensor 114, and a control device119. The first pressure sensor 98 measures a pressure in the surge tank96. Each cover member 102 is attached to an exhaust port 100 of thecorresponding cylinder (or cylinder head 76) so as to close the innerspace of the port 100 and isolate the same from the ambient air. Each Oring 104 is employed to improve the airtightness between thecorresponding cover member 102 and the corresponding exhaust port 100.Each second pressure sensor 106 measures a pressure in the exhaust port100 of the corresponding cylinder. The first A/D converter 110 includesan amplifier for amplifying an output signal of the first sensor 98, andeach second A/D converter 112 includes an amplifier for amplifying anoutput signal of the corresponding second sensor 106. The crank-shaftangle sensor 114 measures an angular phase of the crank shaft 18.

[0143] The control device 119 includes a microcomputer (not shown) whichincludes a central processing unit (CPU), a read only memory (ROM), anda random access memory (RAM) and which functions as a fault finder 117for finding a fault with the assembling of the engine 90, based on therespective output signals supplied from the pressure sensors 98, 106 viathe A/D converters 110, 112, and supplied from the crank-shaft anglesensor 114. The control device 119 additionally includes a display 118for displaying the result of operation of the fault finder 117. Therespective inner spaces of the intake ports 92, the intake manifolds 94,and the surge tank 96 cooperate with one another to provide an externalintake-valve side space which communicates with the intake valves 50;and each of the respective inner spaces of the exhaust ports 100provides an external exhaust-valve side space which communicates withthe corresponding pair of intake valves 50. Each exhaust-valve sidespace is defined by closing an outlet of the exhaust port 100 from thecylinder head 76 of the corresponding cylinder. The intake-valve sidespace is not closed in the present embodiment. However, it may beclosed. Otherwise, the intake-valve side space may be defined by theinner space of each intake port 92 only, or the respective inner spacesof the intake ports 92 and the intake manifolds 94. In the first case,six first pressure sensors 98 whose number is equal to that of thecylinders are needed; and in the second case, two first pressure sensors98 whose number is equal to that of the intake manifolds 94 are needed.

[0144] As shown in FIG. 5, the engine 90 to be tested is fixed on a base120, and is accurately rotated at a constant speed by a drive motor 125to which the crank shaft 18 of the engine 90 is connected via a coupling122 and a drive shaft 124. The drive shaft 124 is supported by bearings126, 128 fixed to the base 120. When the drive motor 125 is rotatedunder control of the control device 119, the engine 90 is rotated in a“cool” state, and the pressure sensors 98, 106 supply their outputsignals to the control device 119, so that the fault finder 117 may finda fault with the assembling of the engine 90.

[0145] When the engine 90 is rotated by the drive motor 125, each valve48, 50 opens and closes as the angular phase of the crank shaft 18changes. When the rotation speed of the motor 125 becomes constant andaccordingly the respective pressures in the six cylinders regularlycyclically change, the respective outputs of the first and secondpressure sensors 98, 106 change as shown in the graph of FIG. 6, if theengine 90 has no assembling fault or defect. FIG. 6 shows the change ofposition, PP, of the piston 10 in the corresponding cylinder (indicatedat #1 in the graph), the change of exhaust pressure, P_(EX),corresponding to the piston or cylinder #1 detected by the correspondingsecond pressure sensor 106, and the change of intake pressure, P_(IN),which is common to all the six cylinders #1 to #6 and is detected by thefirst sensor 98. The engine 90 is a V6 engine, and has the threecylinders #1, #3, #5 in the left bank thereof and has the threecylinders #2, #4, #6 in the right bank thereof. The cylinder #2 isassociated with the piston 12. When the V6 engine 90 automaticallyrotates in a “hot” state because of explosion or combustion in the sixcylinders #1 to #6, the combustion sequentially occurs in the cylinders#1 to #6, for example, in the order of description.

[0146] First, the change of the exhaust pressure P_(EX) (#1) will bedescribed below. When the crank-shaft angle, Θ_(crank), detected by theangle sensor 114 takes an angle, Θ_(EXopen), as the crank shaft 18 isrotated by the motor 125, the exhaust valve 48 associated with thecylinder #1 starts opening. At this time, the piston 10 is moving towardits bottom dead center or position, BDC, and the air in the exhaust port100 starts entering the cylinder #1. Accordingly the exhaust pressureP_(EX) changes from a constant state in which the exhaust pressure takesa constant value, P_(EXconst), to a decreasing state. The crank shaftangle Θ_(crank)=Θ_(EXopen) will be referred to as the exhaust-pressuredecrease-start angle, Θ_(EXdec). After the piston 10 passes through itsbottom dead position BDC and is back to the same position as theposition at the timing at which the valve 48 started opening, the air inthe cylinder #1 and the exhaust port 100 is compressed and accordinglythe exhaust pressure P_(EX) starts increasing. The exhaust pressureP_(EX) takes a maximal value, P_(EXmax), when the angle Θ_(crank) takesan angle, Θ_(INopen), and the intake valve 50 starts opening. The angleΘ_(crank)=Θ_(INopen) will be referred to as the exhaust-pressuremaximal-value angle, Θ_(EXmax). Subsequently, after the intake valve 50opens, the exhaust pressure P_(EX) quickly decreases and then becomesconstant when the angle Θ_(crank) takes an angle, Θ_(EXclose), and theexhaust valve 48 closes. The angle Θ_(crank)=Θ_(EXclose) will bereferred to as the exhaust-pressure constant-start angle, Θ_(EXconst).While the exhaust valve 48 closes, the exhaust pressure P_(EX) takes theconstant value P_(EXconst). Then, when the angle Θ_(crank) takes anangle, Θ_(INclose), the intake valve 50 closes. In the followingdescription, it is assumed that a maximal exhaust pressure valueP_(EXmax) measured from a normal engine with no assembling fault isequal to 100. The exhaust and intake pressure values P_(EX), P_(IN) willbe expressed in terms of values relative to the maximal valueP_(EXmax)=100. For example, a constant exhaust pressure valueP_(EXconst) measured from a normal engine is about 10. The rotationspeed of the drive motor 125 may be selected at any desirable constantvalue, or may be changed to two or more values, as needed, in a singletest.

[0147] The six exhaust pressures P_(EX) are measured from the sixcylinders #1 to #6, respectively, independently of one another. Thesingle intake pressure P_(IN) is measured commonly to all the cylinders#1 to #6. FIG. 6 shows six changes of the intake pressure P_(IN) whichcorrespond to the respective opening and closing of the six pairs ofintake valves 50 of the six cylinders #1 to #6. Those six changessequentially occur at a regular interval of angle in each cycle (onecycle=720 degrees) of the crank-shaft angle Θ_(crank). Hereinafter,there will be described the change of the intake pressure P_(IN) whichcorresponds to the opening and closing of the pair of intake valves 50of the cylinder #1 as a representative of all the cylinders #1 to #6.

[0148] When the crank-shaft (“CS”) angle Θ_(crank) takes the angleΘ_(INopen), the intake valves 50 start opening. Hence, the compressedair in the first cylinder #1 and the exhaust port 100 flows into theintake manifold 94, so that the pressure in the manifold 94 startsincreasing. Although at this time the air in the manifold 94 is beingsucked into the sixth cylinder #6, the amount of flow of air from themanifold 94 into the cylinder #6 is smaller than the amount of flow ofair from the cylinder #1 and the exhaust port 100 into the manifold 94,the pressure in the manifold 94 starts increasing. The angleΘ_(crank)=Θ_(INopen) will be referred to as the intake-pressureincrease-start angle, Θ_(INinc). When the piston of the cylinder #1takes a position PP near an upper dead position, TDC, the amount of flowof air from the cylinder #1 and the exhaust port 100 into the manifold94 which is decreasing because the pressure in the cylinder #1 and theexhaust port 100 is decreasing and the respective clearances of the pairof exhaust valves 48 are decreasing is just balanced by the amount offlow of air from the manifold 94 into the cylinder #6. Subsequently, theformer amount becomes smaller than the latter amount. Thus, the intakepressure P_(IN) takes a maximal value. The CS angle Θ_(crank) at thattiming will be referred to as the intake-pressure maximal-pressureangle, Θ_(INmax). After the position PP of the piston of the cylinder #1takes the upper dead position TDC, the volume of the cylinder #1 startsincreasing. This contributes to decreasing the intake pressure P_(IN).FIG. 6 shows that the intake pressure PIN contains six changes each ofwhich occurs in the above-described manner at a regular interval ofangle Θ_(crank), 120 degrees.

[0149] In the case where the engine 90 is a normal one, that is, anormally assembled one, the six exhaust-pressure signals P_(EX) providedby the six second pressure sensors 106 and a crankshaft (“CS”) referencesignal provided by the CS angle sensor 114 change with respect to the CSangle Θ_(crank) as shown in the graph of FIG. 7. The CS reference signalis a pulse signal containing two pulses per cycle, i.e., per 720 degreesof angle Θ_(crank). In the present embodiment, the CS angle sensor 114includes a passing member provided at a position on the outercircumferential surface of a timing roller (not shown) which is providedintegrally with the crank pulley 20, and a pick-up device such as anelectromagnetic pick-up which detects a timing at which the passingmember passes therethrough. However, it is not essential that thepresent engine testing method employ the sensor 114 of that sort.Recently, almost all engines are provided with such sensors whichcorrespond to the sensor 114, though those sensors may be disposed atdifferent positions. When the present method is carried out on engineswhich have no such sensors, a reflection-type photoelectric switch or aproximity switch may be employed to detect an angular phase of the crankpulley 20 or the crank shaft 18 which is rotating. The six exhaustpressure signals P_(EX) change in substantially the same manner thoughthose changes occur at a regular interval of angle Θ_(crank), 120degrees. When the engine 90 shows the signals as shown in FIG. 7, theengine 90 is a normal one, that is, has no fast or slow crank pulley, nofast or slow cam pulley, no fast or slow driven gear, no larger orsmaller valve clearance, or no compression-ring missing.

[0150] The fault finder 117 successively measures the time intervalbetween each pair of successive pulses of the CS reference signalsupplied from the SC angle sensor 114, and identifies that the rotationspeed of the engine 90 has become steady or constant when the measuredtime intervals become substantially constant. Then, the fault finder 117reads in respective pressure signals provided by the pressure sensors98, 106 via the A/D converters 110, 112, at a very small regularinterval of time, and analyses respective changes of those pressuresignals with respect to pressure and time. Consequently the fault finder117 has the function of identifying predetermined conditions of theexhaust pressures P_(EX) and the intake pressure P_(IN), such as theexhaust-pressure constant value P_(EXconst), the start of decreasing ofthe exhaust pressure P_(EX), the exhaust-pressure maximal valueP_(EXmax), the start of the exhaust-pressure constant value P_(EXconst),the start of increasing of the intake pressure P_(IN), theintake-pressure maximal value P_(INmax), etc., and has the function ofdetermining the essential that the present engine testing method employthe sensor 114 of that sort. Recently, almost all engines are providedwith such sensors which correspond to the sensor 114, though thosesensors may be disposed at different positions. When the present methodis carried out on engines which have no such sensors, a reflection-typephotoelectric switch or a proximity switch may be employed to detect anangular phase of the crank pulley 20 or the crank shaft 18 which isrotating. The six exhaust pressure signals P_(EX) change insubstantially the same manner though those changes occur at a regularinterval of angle Θ_(crank), 120 degrees. When the engine 90 shows thesignals as shown in FIG. 7, the engine 90 is a normal one, that is, hasno fast or slow crank pulley, no fast or slow cam pulley, no fast orslow driven gear, no larger or smaller valve clearance, or nocompression-ring missing.

[0151] The fault finder 117 successively measures the time intervalbetween each pair of successive pulses of the CS reference signalsupplied from the SC angle sensor 114, and identifies that the rotationspeed of the engine 90 has become steady or constant when the measuredtime intervals become substantially constant. Then, the fault finder 117reads in respective pressure signals provided by the pressure sensors98, 106 via the A/D converters 110, 112, at a very small regularinterval of time, and analyses respective changes of those pressuresignals with respect to pressure and time. Consequently the fault finder117 has the function of identifying predetermined conditions of theexhaust pressures P_(EX) and the intake pressure P_(IN), such as theexhaust-pressure constant value P_(EXconst), the start of decreasing ofthe exhaust pressure P_(EX), the exhaust-pressure maximal valueP_(EXmax), the start of the exhaust-pressure constant value P_(EXconst),the start of increasing of the intake pressure P_(IN), theintake-pressure maximal value P_(INmax), etc., and has the function ofdetermining the respective timings of occurrence of those predeterminedconditions. In addition, based on the relationship between the CSreference signal and the CS angle Θ_(crank) that twice the time intervalbetween two pulses of the reference signal is equal to 720 degrees ofthe angle Θ_(crank), the fault finder 117 determines theexhaust-pressure decrease-start angle Θ_(EXdec), the exhaust-pressuremaximal-value angle Θ_(EXmax), the exhaust-pressure constant-start angleΘ_(EXconst), the intake-pressure increase-start angle Θ_(INinc), theintake-pressure maximal-value angle Θ_(INmax), etc. Since thosefunctions of the fault finder 117 are well known as waveform analysistechniques in the art, and since the details of those functions are notessential for understanding the present invention, no furtherdescription is provided.

[0152] Next, there will be described the change of the exhaust pressuresP_(EX) or the intake pressure P_(IN) in the case where each of variousfaults occurs to the engine. In the following description, the symbol(prime) “′” is added when reference is made to each of values of thepressures P_(EX), P_(IN) and the CS angle Θ_(crank) obtained when theengine has a fault, so as to be distinguishable from those obtained whenthe engine is normal.

[0153] First, the faults with the clearance of the intake valve 50 willbe described below.

[0154]FIG. 8 shows a graph representing the change of the exhaustpressure P_(EX) of each cylinder, indicated at solid line, when each ofthe two intake valves 50 of the cylinder has a correct clearance, andthe change of the exhaust pressure P_(EX), indicated at broken line,when one of the two intake valves 50 has a correct clearance but theother's clearance is too small. In the case where the intake-valveclearance is small, the intake valve 50 starts opening too early, andaccordingly the fault finder 117 identifies an exhaust-pressuremaximal-value angle Θ_(EXmax)′ which is smaller than the normal orreference angle Θ_(EXmax). The difference between the two anglesΘ_(EXmax)′, Θ_(EXmax) will be referred to as the exhaust-pressuremaximal-value angle difference, Γ(=Θ_(EXmax)′−Θ_(EXmax)). When theintake-valve clearance is smaller than the correct value, the differenceΓ takes a negative value.

[0155] The smaller the intake-valve clearance is than the correct value,the smaller the difference Γ is. Since the intake valve 50 startsopening earlier when the valve clearance is smaller than the correctvalue, the pressure of the air compressed by the piston in the cylinderis lower than a normal pressure, and accordingly the fault finder 117identifies an exhaust-pressure maximal value P_(EXmax)′ which is smallerby the absolute value of a difference, α, than the normal or referencevalue P_(EXmax). In addition, since the exhaust-pressure maximal valueP_(EXmax)′ is smaller and simultaneously the time duration after one ofthe two intake valves 50 opens and before the exhaust valve 48 closes islonger, the finder 117 identifies an exhaust-pressure constant valueP_(EXconst)′ which is smaller by the absolute value of a difference, β,than the normal or reference value P_(EXconst). In the example shown inFIG. 8, as the piston moves in the cylinder and the volume of thecylinder increases, the air in the intake manifold 94 is sucked into thecylinder. Accordingly, the exhaust-pressure constant value P_(EXconst)′takes a negative value. The smaller the intake-valve clearance is, thesmaller the differences α, β are like the difference Γ. Hereinafter, thedifference α(=P_(EXmax)′−P_(EXmax)) will be referred to as theexhaust-pressure maximal-value difference, and the differenceβ(=P_(EXconst)′−P_(EXconst)) will be referred to as the exhaust-pressureconstant-value difference. Since the differences α, β, Γ can takepositive and negative values, the absolute values of those differenceswill be used in the following description for the purpose of easierunderstanding, so long as circumferences allow. This applies to otherangle differences which will be described later.

[0156]FIG. 9 shows a graph representing the change of the exhaustpressure P_(EX) of each cylinder, indicated at solid line, when each ofthe two intake valves 50 of the cylinder has a correct clearance, andthe change of the exhaust pressure P_(EX), indicated at broken line,when one of the two intake valves 50 has a correct clearance but theother's clearance is too large. In the case where the intake-valveclearance is large, the intake valve 50 starts opening later.Accordingly the fault finder 117 identifies an exhaust-pressuremaximal-value angle Θ_(EXmax)′ which is larger than the normal orreference angle Θ_(EXmax) by the absolute value of a difference Γ. Inaddition, since the pressure of the air compressed by the piston in thecylinder is higher than the normal pressure, the fault finder 117identifies an exhaust-pressure maximal value P_(EXmax)′ which is greaterby the absolute value of a difference α than the reference valueP_(EXmax). In addition, since the exhaust-pressure maximal valueP_(EXmax)′ is greater and simultaneously the time duration after one ofthe two intake valves 50 opens and before the exhaust valve 48 closes isshorter, the finder 117 identifies an exhaust-pressure constant valueP_(EXconst)′ which is greater by the absolute value of a difference βthan the reference value P_(EXconst).

[0157]FIG. 10 shows a graph representing the change of the intakepressure P_(IN) when each of the two intake valves 50 of each cylinderhas a correct clearance, the change of the intake pressure P_(IN) whenone of the two intake valves 50 has a correct clearance but the other'sclearance is too small (hereinafter, abbreviated to “when theintake-valve clearance is small”), and the change of the intake pressureP_(IN) when one of the two intake valves 50 has a correct clearance butthe other's clearance is too large (hereinafter, abbreviated to “whenthe intake-valve clearance is large”). Since the timing of opening ofone of the two intake valves 50 of the cylinder #1 changes, the finder117 identifies an intake-pressure maximal-value angle Θ_(INmax), whichdiffers by a difference, Λ, from the reference value Θ_(INmax), Thedifference Λ(=Θ_(INmax)′−Θ_(INmax)) will be referred to as theintake-pressure maximal-value-angle difference. In addition, the finder117 identifies an intake-pressure increase-start angle Θ_(INinc)′ whichdiffers by a difference, Ψ, from the reference value Θ_(INinc), like thedifference Λ. The difference Ψ(=Θ_(INinc)′−Θ_(INinc)) will be referredto as the intake-pressure increase-start-angle difference. The smalleror the larger the intake-valve clearance is, the smaller or the largerthe differences Λ, Ψ are like the differences Γ, α, β.

[0158] Next, there will be described the faults with the clearance ofthe exhaust valve 48.

[0159]FIG. 11 shows a graph representing the change of the exhaustpressure P_(EX) of each cylinder, indicated at solid line, when each ofthe two exhaust valves 48 of the cylinder has a correct clearance, andthe change of the exhaust pressure P_(EX), indicated at broken line,when one of the two exhaust valves 48 has a correct clearance but theother's clearance is too small (hereinafter, abbreviated to “when theexhaust-valve clearance is small). When the exhaust-valve clearance issmall, the other exhaust valve 48 starts opening earlier. Accordinglythe fault finder 117 identifies an exhaust-pressure decrease-start angleΘ_(EXdec)′ which is smaller by a difference, Φ, than the reference angleΘ_(EXdec). The difference Φ(=Θ_(EXdec)′−Θ_(EXdec)) will be referred toas the exhaust-pressure decrease-start-angle difference. In addition,the fault finder 117 identifies an exhaust-pressure constant-start angleΘ_(EXconst), which is greater by a difference, Σ, than the referencevalue Θ_(EXconst). The difference Σ(=Θ_(EXconst)′−Θ_(EXconst)) wereferred to as the exhaust-pressure constant-start-angle difference. Thetwo differences Φ, Σ are substantially equal to each other. Since theexhaust valve 48 closes later, the finder 117 identifies anexhaust-pressure constant value P_(EXconst)′ which is smaller by theabsolute value of a difference β than the reference value P_(EXconst).In addition, since the amount of air supplied to the exhaust port 100 issmaller, the finder 117 identifies an exhaust-pressure maximal valueP_(EXmax)′ which is smaller by the absolute value of a difference α thanthe reference value P_(EXmax).

[0160]FIG. 12 shows a graph representing the change of the exhaustpressure P_(EX) of each cylinder, indicated at solid line, when each ofthe two exhaust valves 48 of the cylinder has a correct clearance, andthe change of the exhaust pressure P_(EX), indicated at broken line,when one of the two exhaust valves 48 has a correct clearance but theother's clearance is too large (hereinafter, abbreviated to “when theexhaust-valve clearance is large”). When the exhaust-valve clearance islarge, the other exhaust valve 48 opens later and closes earlier.However, the one exhaust valve 48 opens and closes normally. Accordinglythe fault finder 117 identifies exhaust-pressure decrease-start,maximal-value, and constant-start angles Θ_(Exdec)′, Θ_(EXmax)′,Θ_(EXconst)′ which are substantially the same as the reference valuesΘ_(EXdec), Θ_(EXmax), Θ_(EXconst), respectively. However, since theexhaust valve 48 whose clearance is large closes earlier, the finder 117identifies an exhaust-pressure constant value P_(EXconst)′ which isgreater by a difference β than the reference value P_(EXconst). Inaddition, since the amount of air supplied to the exhaust port 100 islarger, the finder 117 identifies an exhaust-pressure maximal valueP_(EXmax)′ which is greater by a difference a than the reference valueP_(EXmax). The faults with the exhaust-valve clearance do notsubstantially influence the intake-pressure increase-start angleΘ_(INinc) or the intake-pressure maximal-value angle Θ_(INmax).

[0161] Next, there will be described the missing of the compression ring144.

[0162] As shown in FIG. 4, the piston of each cylinder has a piston ring134 which includes a top ring 136, a second ring 138, and an oil ring140. The top ring 136 and the second ring 138 cooperate with each otherto provide the compression ring 144 which maintains the air tightnessbetween the piston and the cylinder and thereby maintains theperformance of the engine 90. If at least one of the top ring 136 andthe second ring 138 is missing, the function of the compression ring 144to maintain the air tightness between the piston and the air cylinderlowers. Then, the fault finder 117 identifies that the absolute value ofan exhaust-pressure maximal value P_(EXmax)′ smaller than that of thereference value P_(Exmax), and identifies exhaust-pressure maximal-valueand constant-start angles Θ_(EXmax)′, Θ_(EXconst)′, which aresubstantially the same as the reference values Θ_(EXmax), Θ_(EXconst),respectively.

[0163]FIG. 13 shows a graph representing the change of the exhaustpressure P_(EX) of each cylinder when both of the two rings 136, 138 arenormally set on the piston, and the change of the exhaust pressureP_(EX) when either one of the two rings 136, 138 is missing(hereinafter, abbreviated to “when the compression-ring missingoccurs”). When the compression-ring missing occurs, the finder 117identifies an exhaust-pressure maximal value P_(EXmax)′ which is smallerby the absolute value of a difference α than the reference valueP_(EXmax). When both of the two rings 136, 138 are missing, the finder117 may find the missing by identifying a still smaller exhaust-pressuremaximal value P_(EXmax)′. However, when the missing of either one of thetwo rings 136, 138 is found, the engine 90 is taken apart and thenre-assembled. Thus, the finder 117 need not find the missing of both ofthe two rings 136, 138.

[0164] Next, there will be described the fast or slow state of the campulley 24, 26 and the fast or slow state of the crank pulley 20.

[0165]FIG. 14 shows respective changes of the six exhaust pressuresP_(EX) corresponding to the six pistons or cylinders #1 to #6 when one26 of the cam pulleys 24, 26 is faster by one tooth than the normal,other cam pulley 24, and FIG. 15 shows respective changes of the sixexhaust pressures P_(EX) corresponding to the six cylinders #1 to #6when one 26 of the cam pulleys 24, 26 is slower by one tooth than thenormal, other cam pulley 24. In those cases, the finder 117 identifiesthat respective exhaust-pressure decrease-start, maximal-value, andconstant-start angles Θ_(EXdec)′, Θ_(EXmax)′, Θ_(EXconst)′ of theeven-numbered cylinders #2, #4, #6 are different from the referencevalues Θ_(EXdec), Θ_(EXmax), Θ_(EXconst), respectively. As can beunderstood from this, when only one of the respective cam pulleys 24, 26of the left and right banks is fast or slow, all the angles Θ_(EXdec)′,etc. of the odd- or even-numbered cylinders #1, #3, #5, or #2, #4, #6differ from the reference values Θ_(Exdec), Θ_(EXmax), Θ_(EXconst),respectively.

[0166] When the crank pulley 20 is fast or slow, the finder 117identifies that respective exhaust-pressure decrease-start,maximal-value, and constant-start angles Θ_(EXdec)′, Θ_(EXmax)′,Θ_(EXconst)′ of all the cylinders #1 to #6 are different from thereference values Θ_(EXdec), Θ_(EXmax), Θ_(EXconst), respectively, likewhen both of the two cam pulleys 24, 26 are slow or fast. That is, whenthe crank pulley 20 is fast, the angles Θ_(EXdec)′, etc. differ from thereference values Θ_(EXdec), etc., like when both of the two cam pulleys24, 26 of the two banks are slow, and vice versa. More specifically,when the crank pulley 20 is slow by one tooth, all the exhaust pressuresP_(EX) corresponding to the cylinders #1 to #6 change like those of theeven-numbered cylinders #2, #4, #6 shown in FIG. 14 and, when the crankpulley 20 is fast by one tooth, all the exhaust pressures P_(EX)corresponding to the cylinders #1 to #6 change like those of theeven-numbered cylinders #2, #4, #6 shown in FIG. 15.

[0167]FIG. 16 shows the change of the intake pressure P_(IN) when theright cam pulley 26 is fast by one tooth, the change of the intakepressure P_(IN) when the right cam pulley 26 is slow by one tooth, thechange of the intake pressure P_(IN) when the crank pulley 20 is fast byone tooth, and the change of the intake pressure P_(IN) when the crankpulley 20 is slow by one tooth. When the right cam pulley 26 is fast orslow by one tooth, the respective changes of the intake pressure P_(IN)which represent the respective opening and closing of the even-numberedcylinders #2, #4, #6 occur at different angles than the referenceangles. On the other hand, when the crank pulley 20 is fast or slow, therespective changes of the intake pressure P_(IN) which represent therespective opening and closing of all the cylinders #1 to #6 occur atdifferent angles than the reference angles.

[0168]FIG. 17 shows the change of the exhaust pressure P_(EX) of eachcylinder when the crank pulley 20 is slow by one tooth, or the change ofthe exhaust pressure P_(EX) of one cylinder when one of the cam pulleys24, 26 which corresponds to the one cylinder is fast by one tooth. Inthis case, the fault finder 117 identifies exhaust-pressuredecrease-start, maximal-value, and constant-start angles Θ_(EXdec)′,Θ_(EXmax)′, Θ_(EXconst)′ which are smaller by differences Φ, Γ, Σ thanthe reference values Θ_(EXdec), Θ_(EXmax), Θ_(EXconst), respectively,and that those differences Φ, Γ, Σ are substantially equal to oneanother. The intake valves 50 start opening earlier, that is, as shownin FIG. 6, start opening when the piston is nearer to the bottom deadposition BDC. Thus, the finder 117 identifies the exhaust-pressuremaximal value P_(EXmax)′ which is smaller by the absolute value of adifference a than the reference value P_(EXmax). However, the finder 117identifies the exhaust-pressure constant value P_(EXconst)′ which issubstantially the same as the reference value P_(EXconst).

[0169] In the case where the cam pulley 24, 26 is fast by one tooth, thedifferences Φ, Γ, Σ are equal to a negative angle corresponding to onetooth of the cam pulley 24, 26, that is, −7.5 degrees (=−360(degrees)/48 (teeth)) in terms of rotation angle of the cam pulley 24,26. This angle corresponds to 15 degrees in terms of rotation angle ofthe crank pulley 20. Meanwhile, in the case where the crank pulley 20 isslow by one tooth, the differences Φ, Γ, Σ are equal to a negative anglecorresponding to one tooth of the crank pulley 20, that is, −15 degrees(=−360 (degrees)/48 (teeth)) in terms of rotation angle of the crankpulley 20. As far as the cylinders #2, #4, #6 of the right bank areconcerned, the exhaust pressures P_(EX) change in the same manner bothwhen the right cam pulley 26 is fast by one tooth and when the crankpulley 20 is slow by one tooth. Therefore, the finder 117 identifiesthat the exhaust pressures P_(EX) corresponding to the three cylinders#2, #4, #6 of the right bank take substantially the same maximal valueP_(EXmax)′ and the same maximal-value angle difference Γ in both theabove-indicated two cases.

[0170]FIG. 18 shows the change of the exhaust pressure P_(EX) of each ofthe six cylinders #1 to #6 when the crank pulley 20 is one tooth fast,and the change of the exhaust pressure P_(EX) of each of the threecylinders corresponding to one of the cam pulleys 24, 26 which is onetooth slow. In this case, the fault finder 117 identifiesexhaust-pressure decrease-start, maximal-value, and constant-startangles Θ_(EXdec)′, Θ_(EXmax)′, Θ_(EXconst)′ which are greater by theabsolute values of differences Φ, Γ, Σ than the reference valuesΘ_(EXdec), Θ_(EXmax), Θ_(EXconst), respectively, and that thosedifferences Φ, Γ, Σ are substantially equal to one another.

[0171] The intake valves 50 of the cylinders start opening later than innormal cases. As shown in FIG. 6, the intake valves 50 start openingwhen the pistons are nearer to their top dead positions TDC. Thus, thefinder 117 identifies an exhaust-pressure maximal value P_(EXmax)′ whichis greater by the absolute value of a difference α than the referencevalue P_(EXmax), However, the finder 117 identifies an exhaust-pressureconstant value P_(EXconst)′ which is substantially the same as thereference value P_(EXconst).

[0172] When the crank pulley 20 is one tooth fast or when one of the campulleys 24, 26 is one tooth slow, the differences Φ, Γ, Σ are equal to apositive angle corresponding to one tooth of the cam pulleys 24, 26,that is, 7.5 degrees (=360 (degrees)/48 (teeth)) in terms of rotationangle of the cam pulley 24, 26, that is, 15 degrees (=360 (degrees)/24(teeth)) in terms of rotation angle of the crank pulley 20. As far asthe cylinders #2, #4, #6 of the right bank are concerned, the exhaustpressures P_(EX) change in the same manner both when the right campulley 26 is one tooth slow and when the crank pulley 20 is one toothfast. Therefore, the finder 117 identifies that the respective exhaustpressures P_(EX) of the three cylinders #2, #4, #6 of the right banktake substantially the same maximal value P_(EXmax)′ and maximal-valueangle difference Γ in both the above-indicated two cases.

[0173] Next, there will be described the case where one of the drivengears 40, 42 is fast or slow.

[0174]FIG. 19 is a graph showing the CS reference signal and therespective changes of the six exhaust pressures P_(EX) when the rightdriven gear 42 is one tooth fast, and FIG. 20 is a graph showing the CSreference signal and the respective changes of the six exhaust pressuresP_(EX) when the right driven gear 42 is one tooth slow. As is apparentfrom those graphs, the changes of the exhaust pressures P_(EX) of thethree cylinders of the right bank differ from those obtained from anormal engine. Further detailed description will be made later.

[0175]FIG. 21 is a graph showing the change of the intake pressureP_(IN) when the right driven gear 42 is one tooth fast or slow. As isapparent from the graph, when the right driven gear 42 is one toothfast, the finder 117 identifies that respective intake-pressuremaximal-value and increase-start angles Θ_(INmax)′, Θ_(INinc)′ of theeven-numbered cylinders #2, #4, #6 are smaller than the reference valuesΘ_(INmax), Θ_(INinc), respectively. Contrarily, when the right drivengear 42 is one tooth slow, the finder 117 identifies 55 that respectiveintake-pressure maximal-value angles Θ_(INmax)′ of the even-numberedcylinders #2, #4, #6 are greater than the reference value Θ_(INmax), Onthe other hand, when the left driven gear 40 is one tooth fast or slow,the finder 117 identifies that the respective changes of the intakepressure P_(IN) which correspond to the odd-numbered cylinders #1, #3,#5 differ from those obtained from a normal engine.

[0176]FIG. 22 is a graph showing the change of the exhaust pressureP_(EX) of each of the six cylinders when the engine 90 has no fault, andthe change of the exhaust pressure P_(EX) of each of the three cylindersof the right bank when the right driven gear 42 is one tooth fast. Thedriven gear 42 defines the timing at which the intake valves 50 of theright bank open and close. Since the gear 42 is one tooth fast, thefinder 117 identifies an exhaust-pressure maximal-value angle Θ_(EXmax)′which is smaller than the reference value Θ_(EXmax) by an anglecorresponding to one tooth of the gear 42. Since in the presentembodiment the number of teeth of the gears 40, 42 is forty, the angleis 9 degrees (=360 (degrees)/40 (teeth)) in terms of rotation angle ofthe gear 42. This angle corresponds to 18 degrees in terms of rotationangle of the crank pulley 20. The finder 117 identifies that respectiveexhaust-pressure maximal and constant values P_(EXmax)′, P_(EXconst)′ ofthe even-numbered cylinders #2, #4, #6 are smaller by the absolutevalues of differences α, β than the reference values P_(EXmax),P_(EXconst), respectively. In addition, the finder 117 finds respectiveexhaust-pressure constant-start angles Θ_(EXconst)′ which are smaller bya difference Γ than the reference value Θ_(EXconst). In a normal engine,the angles Θ_(EXconst) correspond to the closing of the exhaust valves48. However, when the driven gear 42 is one tooth fast, theexhaust-pressure maximal-value angles Θ_(EXmax)′ are smaller than thereference value Θ_(EXmax), and accordingly the exhaust pressures P_(EX)become equilibrium with the respective pressures in the cylinders beforethe exhaust valves 48 close.

[0177]FIG. 23 is a graph showing the change of the exhaust pressureP_(EX) of each of the six cylinders when the engine 90 has no fault, andthe change of the exhaust pressure P_(EX) of each of the three cylindersof the right bank when the right driven gear 42 is one tooth slow. Inthis case, contrary to the graph of FIG. 22, the finder 117 identifiesan exhaust-pressure maximal-value angle Θ_(EXmax)′ which is greater by adifference Γ than the reference value Θ_(EXmax). On the other hand, thefinder 117 identifies an exhaust-pressure constant-start angleκ_(EXconst)′ which is substantially the same as the reference valueΘ_(EXconst), that is, identifies that the exhaust-pressureconstant-start-angle difference Σ is zero. Since the exhaust-pressuremaximal-value angles Θ_(EXmax)′ are greater than the reference valueΘ_(EXmax), the finder 117 identifies that respective exhaust-pressuremaximal and constant values P_(EXmax)′, P_(EXconst)′ of theeven-numbered cylinders #2, #4, #6 are greater by the absolute values ofdifferences α, β than the reference values P_(EXmax), P_(EXconst),respectively.

[0178]FIG. 24 is a table showing respective actual values of theexhaust-pressure maximal-value difference α, the exhaust-pressureconstant-value difference β, the exhaust-pressure maximal-value-angledifference Γ, the exhaust-pressure constant-start-angle difference Σ,etc. Those actual values are obtained in the case where just one faultoccurs to the engine 90 and two or more faults do not simultaneouslyoccur to the same 90. The pressure difference values indicated in thetable of FIG. 24 are values relative to the normal or referenceexhaust-pressure maximal value P_(EXmax)=100, and the angle differencevalues indicated in the table are values relative to the CS referencesignal output from the CS angle sensor 114. When the crank pulley 20 isone tooth fast or slow, the values obtained from the right bank are thesame as those obtained from the left bank. However, when one of the campulleys 24, 26 or one of the driven gears 40, 42 is one tooth fast orslow, only the values obtained from one of the two banks whichcorresponds to the fast or slow cam pulley or the fast or slow drivengear differ from those obtained from the normal bank. Although it isvery rare, it is possible that both of the two cam pulleys 24, 26 befast or slow or that both of the two driven gears 40, 42 be fast orslow. The values obtained when the intake-valve or exhaust-valveclearance is small or large continuously change, since the clearancecontinuously changes. The table of FIG. 24 just exemplifies such actualvalues which enable the fault finder 117 to identify the small or largeintake-valve or exhaust-valve clearance.

[0179]FIG. 25 is a flow chart representing the main routine of theassembled engine testing program which is stored in the ROM of the faultfinder 117 and which is carried out by the CPU and the RAM of the finder117. According to the main routine, the fault finder 117 identifies thepresence or absence of an assembling fault of the engine 90, based onthe respective exhaust-pressure maximal values corresponding to the sixpistons or cylinders #1 to #6. If the engine 90 has no fault, the finder117 commands the display 118 (FIG. 26) to indicate that the engine 90has passed the test. On the other hand, if a fault is found, the finder117 identifies or specifies what is the fault and commands the display118 to indicate that the engine 90 has not passed the test and the placewhere the fault has occurred.

[0180] First, at Step S100, the fault finder 117 or the CPU thereofinitializes a flag variable, ‘flag’, to flag=0×00 (i.e., 00000000) and,at Step S102, it initializes a variable, ‘count’, to count=0. At StepS104, the CPU initializes a variable, ‘i’, to i=0 corresponding to thefirst piston #1. The number greater by one than the variable ‘i’ isequal to the number of the current piston.

[0181] Subsequently, at Step S106, the CPU judges whether all therespective absolute values of the exhaust-pressure maximal-valuedifference α[i], the exhaust-pressure constant-value difference β[i],the exhaust-pressure maximal-value-angle difference Γ[i], theexhaust-pressure constant-start-angle difference Σ[i], theexhaust-pressure decrease-start-angle difference Φ[i], theintake-pressure maximal-value-angle difference Λ[i], and theintake-pressure increase-start-angle difference Ψ[i] which are measuredfrom the piston #i+1 are smaller than 3. If a negative judgment is madeat Step S106, the control of the CPU goes to Step S108 to add one to thevariable ‘count’. On the other hand, if a positive judgment is made atStep S106, the control goes to Step S110 to judge whether the variable‘i’ is equal to 5 corresponding to the sixth piston #6. If a negativejudgment is made at Step S110, the control goes to Step S111 to add oneto the variable ‘i’ and then goes back to Step S106.

[0182] As can be understood from FIG. 24, in the case where it isassumed that two or more assembling faults do not simultaneously occur,it can be concluded that if the respective absolute values of thedifferences α, β, etc. are smaller than 3, the test engine 90 hasnormally been assembled without any fault.

[0183] If a positive judgment is made at Step S110, the control of theCPU goes to Step S112 to judge whether the variable ‘count’ is equal to0. If a positive judgment is made at Step S112, the control goes to StepS114 to command the display 118 to light an OK lamp of the display 118indicating that no fault has been found. Thus, the CPU quits the mainroutine. On the other hand, if a negative judgment is made at Step S112,that is, a fault has been found, the control goes to Step S116 to lightan NG lamp of the display 118 indicating that situation. Subsequently,the control goes to Step S118, i.e., a fault identifying or specifyingsubroutine. Step S118 is followed by Step S120 to light a lamp of thedisplay 118 corresponding to the fault specified at Step S118. Then, theCPU quits the main routine.

[0184] The display 118 may have an arrangement as shown in FIG. 26. Inthe figure, reference numeral 200 designates the OK lamp which is litwhen no fault is found. Numeral 202 designates the NG lamp which is litwhen a fault is found. In the case where a fault is found and specified,the control device 119 may light one of the following lamps whichcorresponds to the fault specified: a fast crank-pulley lamp 204, a slowcrank-pulley lamp 206, a fast left-cam-pulley lamp 208, a slowleft-cam-pulley lamp 210, a fast right-cam-pulley lamp 212, a slowright-cam-pulley lamp 214, a fast left-driven-gear lamp 216, a slowleft-driven-gear lamp 218, a fast right-driven-gear lamp 220, and a slowright-driven-gear lamp 222. In addition, the CPU may light, for each ofthe pistons #1 to #6, one of a small intake-valve clearance lamp 224, alarge intake-valve clearance lamp 226, a small exhaust-valve clearancelamp 228, a large exhaust-valve clearance lamp 230, and acompression-ring missing lamp 232. Moreover, in the case where a faultcannot be specified as will be described later, another lampcorresponding to a doubtful fault may be lit. Hereinafter, those lampswill be referred to as the fault lamps.

[0185]FIG. 27 is a flow chart representing the fault specifyingsubroutine of Step S118 of FIG. 25. In the present subroutine, it isassumed that only a single fault occurs if any, that is, two or morefaults do not simultaneously occur. Generally, it is possible that twoor more assembling faults simultaneously occur to a single engine, butthat possibility is very low. Therefore, in almost all cases, thepresent subroutine is effective in specifying the fault. Even if two ormore faults simultaneously occur and accordingly the subroutine providesan incorrect specification of the fault, the main routine does notprovide such a judgment that no fault has been found. Thus, theincorrect specification is permissible.

[0186] In the present fault specifying routine, first, at Step S200, theCPU of the fault finder 117 initializes each of eight flagscorresponding to the above-indicated faults, to 0×00. Hereinafter, thoseflags will be referred to as the fault flags. As shown in FIG. 28, eachof the eight flags comprises one byte data, i.e., eight bits data. If nofault has been found, each flag remains 0×00. The lower four bits of theflag ‘flag_(drvn)’ correspond to the fast and slow states of the leftand right driven gears 40, 42, and the lower four bits of the flag‘flag_(cam)’ correspond to the fast and slow states of the left andright cam pulleys 24, 26. The lower two bits of flag_(crnk) correspondto the fast and slow states of the crank pulley 20. The lower six bitsof the flags ‘flag_(ins)’, ‘flag_(inl)’, ‘flag_(exs)’, ‘flag_(exl)’,‘flag_(ring)’ correspond to the presence or absence of the small andlarge intake-valve clearances, the small and large exhaust-valveclearances, and the compression-ring missing, respectively, of the sixpistons or cylinders #1 to #6. The respective highest (leading) bits ofthe eight flags are doubtful-fault bits each of which may be set to 1 toindicate that a corresponding fault is doubtful but cannot be specified.

[0187] Step S200 is followed by Steps S202 to S214. Step S202 is acrank-pulley test for determining values to be set to the flag‘flag_(crnk)’. Steps S206 and S210 are cam-pulley and driven-gear tests1, 2 for determining values to be set to the flags ‘flag_(cam)’ and‘flag_(drvn)’. Step S214 is a valve-clearance and compression-ring testfor determining values to be set to the flags ‘flag_(ins)’,‘flag_(inl)’, ‘flag_(exs)’, ‘flag_(exl)’, ‘flag_(ring)’. Hereinafter,those steps will be described in detail. If a fault is found at thefirst one of those steps, then the CPU quits the fault specifyingroutine and the remaining step or steps is or are not carried out. Thiscorresponds to the above-indicated assumption that only a single faultoccurs to a single engine 90.

[0188] First, the crank-pulley test at Step S202 of FIG. 27 will bedescribed below.

[0189]FIG. 29 is a flow chart representing the crank-pulley testingsubroutine of Step S202 of FIG. 27. First, at Step S300, the CPU of thefault finder 117 judges whether the respective exhaust-pressuremaximal-value differences α[i] of all the six cylinders #1 to #6 are notsmaller than 3. If a positive judgment is made at Step S300, the controlgoes to Step S302 to set 0×01 to the flag ‘flag_(crnk)’ indicating thatthe crank pulley 20 is fast by one tooth. Then, the CPU quits thepresent subroutine. On the other hand, if a negative judgment is made atStep S300, the control goes to Step S304 to judge whether the respectivedifferences α[i] of all the cylinders #1 to #6 are not greater than −3.If a positive judgment is made at Step S304, the control goes to StepS306 to set 0×02 to the flag ‘flag_(crnk)’ indicating that the crankpulley 20 is slow by one tooth. Then, the CPU quits the subroutine. Onthe other hand, if a negative judgment is made at Step S304, the controldirectly quits the subroutine. The reason why the respective differencesα[i] of all the cylinders #1 to #6 are compared with 3 or −3 at StepS300 or S304 is the same as that described for Step S106 of FIG. 25.However, here, not only the absolute values, but also the positive ornegative signs, of the differences α[i] are utilized for finding thefast or slow state of the crank pulley 20. A negative judgment made atStep S304 indicates that the crank pulley 20 has normally been assembledinto the engine 90, and the fault flag ‘flag_(crnk)’ remains 0×00. Inthis case only, a positive judgment is made at Step S204, and thecontrol goes to Step S206. At Step S300 or S304, the CPU may take intoaccount the detected changes of respective timings of occurrence of acertain pressure condition to the cylinders #1 to #6, for example,respective changes of the exhaust-pressure maximal-value-angledifferences Γ of the cylinders #1 to #6.

[0190]FIG. 30 is a flow chart representing the cam-pulley anddriven-gear test 1 of Step S206 of FIG. 27. This subroutine is carriedout for finding the one-tooth fast state of each of the cam pulleys 24,26 and the driven gears 40, 42. First, at Step S400, the CPU of thefault finder 117 judges whether the respective differences α[i] of thecylinders #1 to #3 of the left bank are not greater than −3. If apositive judgment is made at Step S400, the control goes to Step S402 tojudge whether the respective exhaust-pressure maximal-value-angledifferences Γ of the cylinders #1 to #3 of the left bank are not greaterthan −16.5. If a positive judgment is made at Step S402, the controlgoes to Step S404 to set 0×01 to the flag ‘flag_(drvn)’ indicating thatthe left driven gear 40 is one-tooth fast. On the other hand, if anegative judgment is made at Step S402, the control goes to Step S406 toset 0×01 to the fault flag ‘flag_(cam)’ indicating that the left campulley 24 is one-tooth fast. Then, the CPU quits the present subroutine.The reason why the differences α[i] are compared with −3 at Step S400 orS408 is the same as that described for Steps S300 and S304 of FIG. 29.Step S402 is provided for judging which is one-tooth fast, the left campulley 24 or the left driven gear 40. The threshold value, −16.5,employed at Step S402 is the average of the corresponding twodifferences P, −15 and −18, shown in FIG. 24. Likewise, other thresholdvalues which are employed at other steps are so determined as to be ableto specify the fault.

[0191] On the other hand, if a negative judgment is made at Step S400,the CPU carries out, for the right bank, Steps S408, S410, S412, andS414 corresponding to Steps S400 to S406 for the left bank,respectively. However, at Step S412, the CPU sets 0×04 to the flag‘flag_(drvn)’ indicating that the right driven gear 42 is one-tooth fastand, at Step S414 the CPU sets 0×04 to the flag ‘flag_(cam)’ indicatingthat the right cam pulley 26 is one-tooth fast. On the other hand, if anegative judgment is made at Step S408, the control directly quits thesubroutine. In the last case, a positive a judgment is made at StepS208, and the control goes to Step S210.

[0192]FIG. 31 is a flow chart representing the cam-pulley anddriven-gear test 2 of Step S210 of FIG. 27. This subroutine is carriedout for finding the one-tooth slow state of each of the cam pulleys 24,26 and the driven gears 40, 42. First, at Step S500, the CPU of thefault finder 117 judges whether the respective differences α[i] of thecylinders #1 to #3 of the left bank are greater than 3. If a positivejudgment is made at Step S500, the control goes to Step S502 to judgewhether the respective differences Γ of the cylinders #1 to #3 of theleft bank are greater than 16.5. If a positive judgment is made at StepS502, the control goes to Step S504 to set 0×02 to the flag‘flag_(drvn)’ indicating that the left driven gear 40 is one-tooth slow.On the other hand, if a negative judgment is made at Step S502, thecontrol goes to Step S506 to set 0×02 to the flag ‘flag_(cam)’indicating that the left cam pulley 24 is one-tooth slow. Then, the CPUquits the subroutine. Step S502 is provided for judging which isone-tooth slow, the left cam pulley 24 or the left driven gear 40.

[0193] On the other hand, if a negative judgment is made at Step S500,the CPU carries out, for the right bank, Steps S508, S510, S512, andS514 corresponding to Steps S500 to S506 for the left bank,respectively. However, at Step S512, the CPU sets 0×08 to the flag‘flag_(drvn)’ indicating that the right driven gear 42 is one-tooth slowand, at Step S514 the CPU sets 0×08 to the flag ‘flag_(cam)’ indicatingthat the right cam pulley 26 is one-tooth slow. On the other hand, if anegative judgment is made at Step S508, indicating that the cam pulleys24, 26 and the driven gears 40, 42 have normally been assembled, thecontrol directly quits the subroutine. In the last case, a positivejudgment is made at Step S212, and the control goes to Step S214. Thethreshold values employed at Steps S500 and 508 are determined for thesame reason as that described for those employed at Steps S400 and S408of FIG. 30.

[0194] Although, in the tests 1, 2 shown in FIGS. 30 and 31, the fast orslow states of the cam pulleys 24, 26 and the driven gears 40, 42 arefound based on the exhaust-pressure maximal-value angles Γ of thecylinders #1 to #6, they may be found based on the intake-pressuremaximal-value angles or the intake-pressure increase-start angles of thecylinders #1 to #6. Otherwise, they may be found based on two or more ofthose parameters Γ, Λ, Ψ. In the last case, the tests 1, 2 enjoy higherreliability. In addition, they may be found based on theexhaust-pressure constant-start angles Σ of the cylinders #1 to #6. Inthe last case, the threshold values employed at Steps S402, S410, S502,S510 are replaced with −12, −12, 8, and 8, respectively, and theless-than signs are replaced with greater-than signs, and vice versa.

[0195] In the case where there is no possibility that any fault occursto the assembling of the driven gears 40, 42, it is possible to omit,from the subroutines shown in FIGS. 30 and 31, the steps relating to thedriven gears 40, 42, that is, Steps S404, S412, S504, and S512. In thiscase, a cam-pulley test may be carried out based on only theexhaust-pressure decrease-start angles Φ of the cylinders #1 to #6. Forexample, if all the exhaust-pressure decrease-start angles ( of thethree cylinders of each bank are smaller than −8, the CPU may set, inthe flag ‘flag_(cam)’ a value indicating that the cam pulley 24 or 26 ofthat bank is one-tooth fast and, if those are not smaller than −8, theCPU directly quits the subroutine. In addition, if all the angles Φ ofthe three cylinders of each bank are greater than 8, the CPU may set, inthe flag ‘flag_(cam)’ a value indicating that the cam pulley 24 or 26 ofthat bank is one-tooth slow and, if those are not greater than 8, theCPU directly quits the subroutine.

[0196]FIG. 32 is a flow chart representing the valve-clearance andcompression-ring test of Step S214 of FIG. 27. First, at Step S600, theCPU sets 0×01 to a variable ‘buf’ and, at Step S602, the CPU initializesthe variable ‘i’ to 0 corresponding to the first piston or cylinder #1.Subsequently, at Step S604, the CPU judges whether the exhaust-pressuremaximal-value difference α[i] of the current cylinder is not smallerthan 3. If a positive judgment is made at Step S604, the control goes toStep S606 to judge whether the exhaust-pressure maximal-value-angledifference Γ[i] of the current cylinder is not smaller than 2. only if apositive judgment is made at Step S604, the CPU makes a judgment thatsome fault has occurred to the engine 90. The reason why whether thedifference Γ[i] of the current cylinder is not smaller than 2 is judgedat Step S606 is that, as is apparent from FIG. 24, if the differenceα[i] of the current cylinder is not smaller than 3, the difference Γ[i]of the current cylinder takes 5.4 in the case of a large intake-valveclearance, or 0 in the case of a large exhaust-valve clearance and thatthose two cases is distinguished from each other by comparing thedifference Γ[i] with a value about the average of those two values, 5.4and 0. If a positive judgment is made at Step S606, the control goes toStep S608 to set the logical sum of the flag ‘flag_(inl)’ and thevariable ‘buf’ to the flag ‘flag_(inl)’. Consequently one of the lowersix bits of the flag ‘flag_(inl)’ which corresponds to the currentcylinder is changed to 1 indicating that a fault has occurred to theintake-valve clearance corresponding to the current cylinder. On theother hand, if a negative judgment is made at Step S606, the controlgoes to Step S610 to set the logical sum of the flag ‘flag_(exl)’ andthe variable ‘buf’ to the flag ‘flag_(exl)’.

[0197] Step S608 or S612 is followed by Step S612 to add 1 to thevariable ‘i’ and subsequently by Step S614 to judge whether the variable‘i’ is equal to 6. If a positive judgment is made at Step S614, the CPUquits the present subroutine. On the other hand, if a negative judgmentis made at Step S614, the control goes to Step S616 to change, in thevariable ‘buf’, the bit currently having 1, to 0 and change the next,higher bit currently having 0, to 1, so that the number currentlyindicated by the variable ‘i’ coincides with the number (FIG. 28)assigned to the bit newly changed to 1. Subsequently, the control goesback to Step S604. Thus, the provision of Step S616 ensures that at StepS608 or Step 610 one of the lower six bits of the flag ‘flag_(inl)’ or‘flag_(exl)’ which corresponds to the current cylinder is changed to 1indicating that a fault has occurred to the intake-valve orexhaust-valve clearance corresponding to the current cylinder.

[0198] On the other hand, if a negative judgment is made at Step S604,the control goes to Step S618 to judge whether the difference α[i] ofthe current cylinder is not greater than −3. If a negative judgment ismade at Step S618, the control goes to Step S612. On the other hand, ifa positive judgment is made at Step S618, the control goes to Step S620to judge whether the exhaust-pressure constant-value difference β[i] ofthe current cylinder is not smaller than −5. The reason why whether thedifference β[i] of the current cylinder is not smaller than −5 is judgedat Step S620 is that, as is apparent from FIG. 24, if the differenceα[i] of the current cylinder is not greater than −3, the difference β[i]of the current cylinder takes −16 in the case of a small intake-valveclearance, −10 in the case of a small exhaust-valve clearance, or −1 inthe case of a compression-ring missing and that the compression-ringmissing is distinguished from the other two cases by comparing thedifference β[i] with a value about the average of the two values, −10and −1. If a positive judgment is made at Step S620, the control goes toStep S622 to set the logical sum of the flag ‘flag_(ring)’ and thevariable ‘buf’ to the flag ‘flag_(ring)’. Subsequently, the control goesto Step S612. On the other hand, if a negative judgment is made at StepS620, the control goes to Step S624 to judge whether the difference α[i]of the current cylinder is not greater than −30. If a positive judgmentis made at Step S624, the control goes to Step S626 to set the logicalsum of the flag ‘flag_(ins)’ and the variable ‘buf’ to the flag‘flag_(ins)’. On the other hand, if a negative judgment is made at StepS624, the control goes to Step S628 to set the logical sum of the flag‘flag_(exs)’ and the variable ‘buf’ to the flag ‘flag_(exs)’.Subsequently, the control goes to Step S612. The reason why whether thedifference α[i] of the current cylinder is not greater than −30 isjudged at Step S624 is that, as is apparent from FIG. 24, if thedifference β[i] of the current cylinder is smaller than −5, thedifference α[i] of the current cylinder takes −47 in the case of a smallintake-valve clearance, or −8 in the case of a small exhaust-valveclearance and that those two cases is distinguished from each other bycomparing the difference α[i] with a value about the average of the twovalues, −47 and −8. At Step S624, the test may be carried out based onthe difference β[i] in place of the difference α[i], in particular inthe case where there is no possibility that any compression-ring missingoccurs. In this case, however, the threshold value, −30, employed atStep S624 is replaced by, e.g., −13 which is the average of −16 and −10.

[0199] In the case where it is only required to judge whether theintake-valve clearance is correct, the CPU can make a judgment based ononly the exhaust-pressure maximal-value-angle difference Γ[i] of thecurrent cylinder. For example, if the difference Γ[i] is greater than 2which is about the average of 5.4 and 0, the CPU finds a largeintake-valve clearance and, if the difference Γ[i] is smaller than −3which is about the average of −6.4 and 0, the CPU finds a smallintake-valve clearance. In this case, the difference Γ[i] may bereplaced by the intake-pressure maximal-value-angle difference Λ or theintake-pressure increase-start-angle difference Ψ. In the case where theintake- or exhaust-valve clearance may continuously change, thedifference α[i] or Γ[i] may also change continuously. Meanwhile, in thecase where the intake- or exhaust-valve clearance may stepwise change,the difference α[i] or Γ[i] may also change stepwise. Therefore, it ispreferred to change the criteria employed in the above-described faultfinding tests, depending upon which is the case with the engine 90 to betested.

[0200] Next, there will be described a second embodiment of the presentinvention. The second embodiment is different from the above-describedfirst embodiment in that the fault specifying subroutine of FIG. 27(i.e., Step S118 of FIG. 25) employed in the first embodiment isreplaced by a different fault specifying subroutine employed in thesecond embodiment. The different subroutine is represented by the flowchart of FIG. 33. The engine testing apparatus of FIG. 4 employed in thefirst embodiment is also employed in the second embodiment.

[0201] In the first embodiment, it has been assumed that only a singleassembling fault, if any, occurs to an assembled engine. In contrast, inthe second embodiment, if a plurality of assembling faultssimultaneously occur, at least two of the plurality of faults can befound. The flow chart of FIG. 33 includes Step S700 that is the same asStep S200 of FIG. 27. Step S700 is followed by Step S702, i.e., firsttest 1 as a subroutine and subsequently by Steps S704 and S706, i.e.,second and third tests 2, 3 as subroutines.

[0202] Step S706 is followed by Step S708 that is the same as Step S120of FIG. 25. Hereinafter, the first to third tests 1, 2, 3 will bedescribed below.

[0203]FIG. 34 is a flow chart representing the first test 1 of Step S702of FIG. 33. First, at Step S800, the CPU of the fault finder 117 sets,in the variable ‘i’, an initial value, 0, corresponding to the firstpiston or cylinder #1. Step S800 is followed by Step S802 to identifyone of the following eleven ranges (1) through (11) in which theexhaust-pressure decrease-start-angle difference α[i] of the currentcylinder falls:

[0204] Range (1): −42≦Φ[i]<−32

[0205] Range (2): −32≦Φ[i]<−28

[0206] Range (3): −27≦Φ[i]<−17

[0207] Range (4): −17≦Φ[i]<−13

[0208] Range (5): −12≦Φ[i]<−2

[0209] Range (6): −2≦Φ[i]<2

[0210] Range (7): 3≦Φ[i]<13

[0211] Range (8): 13≦Φ[i]<17

[0212] Range (9): 18≦Φ[i]<28

[0213] Range (10): 28≦Φ[i]<32

[0214] Range (11): 1[i]<−42 or 32≦Φ[i]

[0215] The reason why Step S802 is provided is that as is apparent fromFIG. 24, the difference Φ is produced only when the fast or slow stateof the crank pulley 20, the left cam pulley 24, or the right cam pulley26, or the small exhaust-valve clearance occurs. When the crank pulley20 is one-tooth fast, normal, or one-tooth slow, the difference Φ[i]stepwise changes to 15, 0, or −15, respectively. Likewise, when the leftor right crank pulley 24, 26 is one-tooth fast, normal, or one-toothslow, the difference Φ[i] stepwise changes to 15, 0, or −15,respectively. In the present embodiment, the fault finder 117 judges, ifthe difference Φ[i] of one cylinder falls in the range of −2 to 2, thatthe exhaust-valve clearance corresponding to the cylinder is normal.Therefore, even if the exhaust-valve clearance of one cylinder is judgedas normal, the difference Φ[i] of the cylinder may not be equal to 0 butmay take any value within the range of −2 to 2. In addition, thedifference Φ[i] of each cylinder cannot take a value smaller than −10,even if the exhaust-valve clearance of the cylinder is very small. FIG.40 shows the ten ranges (1) to (10) of the difference (that aredetermined by taking the above-indicated facts into account. The tenranges (1) to (10) are defined by the following fifteen border values:−30 −(10+2), −30±2, −15−(10+2), −15±2, 0−(10+2), 0±2, 15−(10+2), 15±2,30−(10+2), and 30±2. Each of the above eleven ranges (1) to (11)corresponds to the following faults of the crank pulley 20, one of thetwo crank pulleys 24, 26 which corresponds to the current cylinder, andthe exhaust-valve clearance of the current cylinder:

[0216] Range (1): crank pulley 20 one-tooth slow, and cam pulley 24 or26 one-tooth fast, and exhaust-valve clearance small

[0217] Range (2): crank pulley 20 one-tooth slow, and cam pulley 24 or26 one-tooth fast, and exhaust-valve clearance normal

[0218] Range (3): crank pulley 20 one-tooth slow, and cam pulley 24 or26 normal, and exhaust-valve clearance small, or

[0219]  crank pulley 20 normal, and cam pulley 24 or 26 one-tooth fast,and exhaust-valve clearance small

[0220] Range (4): crank pulley 20 one-tooth slow, and cam pulley 24 or26 normal, and exhaust-valve clearance normal, or

[0221]  crank pulley 20 normal, and cam pulley 24 or 26 one-tooth fast,and exhaust-valve clearance normal

[0222] Range (5): crank pulley 20 normal, and cam pulley 24 or 26normal, and exhaust-valve clearance small, or crank pulley 20 one-toothfast, and cam pulley 24 or 26 one-tooth fast, and exhaust-valveclearance small, or

[0223]  crank pulley 20 one-tooth slow, and cam pulley 24 or 26one-tooth slow, and exhaust-valve clearance small

[0224] Range (6): crank pulley 20 normal, and cam pulley 24 or 26normal, and exhaust-valve clearance normal, or crank pulley 20 one-toothfast, and cam pulley 24 or 26 one-tooth fast, and exhaust-valveclearance normal, or

[0225]  crank pulley 20 one-tooth slow, and cam pulley 24 or 26one-tooth slow, and exhaust-valve clearance normal

[0226] Range (7): crank pulley 20 one-tooth fast, and cam pulley 24 or26 normal, and exhaust-valve clearance small, or

[0227]  crank pulley 20 normal, and cam pulley 24 or 26 one-tooth slow,and exhaust-valve clearance small

[0228] Range (8): crank pulley 20 one-tooth fast, and cam pulley 24 or26 normal, and exhaust-valve clearance normal, or

[0229]  crank pulley 20 normal, and cam pulley 24 or 26 one-tooth slow,and exhaust-valve clearance normal

[0230] Range (9): crank pulley 20 one-tooth fast, and cam pulley 24 or26 one-tooth slow, and exhaust-valve clearance small

[0231] Range (10): crank pulley 20 one-tooth fast, and cam pulley 24 or26 one-tooth slow, and exhaust-valve clearance normal

[0232] Range (11): error

[0233] The ranges (1) to (10) are obtained by combining the changes ofthe difference Φ due to the assembling faults with the crank pulley 20and either one of the two cam pulleys 24, 26 and the changes of thedifference Φ due to the assembling faults with the exhaust-valveclearance. As is apparent from FIG. 40, the difference Φ is influencedby the faults with the exhaust-valve clearance independent of the faultswith the crank pulley 20 and the cam pulleys 24, 26.

[0234] The crank pulley 20 assembled into the engine 90 can take eitherone of the three states, i.e., normal, fast, and slow states, andlikewise the left or right cam pulley 24, 26 assembled into the engine90 can take either one of the three states, i.e., normal, fast, and slowstates. Therefore, there are nine possible combinations. Since theexhaust valve clearance can take either one of the two states, i.e.,normal and small states, there are eighteen possible combinations.However, since the difference Φ is similarly influenced by two or moredifferent combinations of the respective states of the crank pulley 20and the cam pulley 24, 26, only the above-indicated ten ranges (1) to(10) (except for the eleventh range (11)) are distinguished from oneanother. That is, there are some cases where the respective states ofthe crank pulley 20 and the cam pulley 24, 26 cannot be specified basedon only the test 1 using the difference Φ. More specifically described,each of the ranges (3), (4), (7), and (8) corresponds to two differentcombinations of the respective states of the crank pulley 20 and the campulley 24, 26, and each of the ranges (5) and (6) corresponds to threedifferent combinations.

[0235] However, since the engine 90 has the left and right cam pulleys24, 26 corresponding to the left and right banks, respectively, thereare 27 possible combinations of the respective states of the crankpulley 20 and the two cam pulleys 24, 26. As is described below, each of12 state combinations out of the 27 state combinations corresponds to asingle combination of the respective differences Φ corresponding to theleft and right banks that is different from the other differencecombinations corresponding to the other state combinations. Thus, eachof the 12 state combinations can be specified or identified from theother state combinations. Moreover, since the exhaust-valve clearancecan take either one of the two states (i.e., normal and small states),there are 54 possible state combinations (obtained by multiplying 27 by2). Since the two states of the exhaust-valve clearance can be specifiedindependent of the respective states of the three pulleys 20, 24, 26,twenty four combinations out of the 54 combinations can be specifiedbased on only the first test 1 using the difference Φ.

[0236] More specifically described, in the case where only therespective states of the crank pulley 20 and the left and right campulleys 24, 26 are taken into account, the difference Φ takes a firstvalue of 0, 15, or −15 when the crank pulley 20 is normal, one-toothfast, or one-tooth slow, respectively, and likewise the difference Φtakes a second value of 0, −15, or 15 when the left or right cam pulley24, 26 is normal, one-tooth fast, or one-tooth slow, respectively.Addition of the first and second values provides 20 differentcombinations of the respective differences Φ corresponding to the leftand right banks. The difference Φ corresponding to each of the left andright banks can take 5 different values, i.e., 0, ±15, and ±30.Accordingly, theoretically, there are 25 possible combinations of thetwo differences Φ corresponding to the two banks. However, since thedifference (absolute value) of the two differences Φ corresponding tothe two banks cannot be greater than 30. Therefore, actually, the 27different combinations of the respective states of the three pulleys 20,24, 26 correspond to the 20 different combinations of the respectivedifferences Φ corresponding to the two banks. The above-indicated 12state combinations each of which can be specified from the othercombinations of the 27 state combinations are as follows (a left valuecorresponds to the left bank, and a right value corresponds to the rightbank): (0, −30), (0, 30), (−15, −30), (−15, 15), (−30, 0), (−30, −15),(−30, −30), (15, −15), (15, 30), (30, 0), (30, 15), and (30, −30). Forexample, the difference combination (0, −30) corresponds to only thestate combination of the crank pulley 20 one-tooth slow, the left campulley 24 one-tooth slow, and the right cam pulley 26 one-tooth fast.

[0237] However, each of the six difference combinations (0, −15), (0,15), (−15, 0), (−15, −15), (15, 0), and (15, 15) corresponds to twostate combinations. For example, the difference combination (0, −15)corresponds to (1) the state combination of the crank pulley 20 normal,the left cam pulley 24 normal, and the right cam pulley 26 one-toothfast and (2) the state combination of the crank pulley 20 one-toothslow, the left cam pulley 24 one-tooth slow, and the right cam pulley 26normal. The difference combination (0, 0) corresponds to three statecombinations (described later). Thus, the 12 state combinations can bespecified from the other 15 state combinations (15=6×2+3×1) that cannotbe specified. However, each of the above-indicated six differencecombinations can be limited to the corresponding two state combinations,and the difference combination (0, 0) can be limited to thecorresponding three state combinations. Thus, such information is veryuseful for the actual engine testing and the subsequent correction ofthe fault or faults.

[0238] Since the two states of the exhaust-valve clearance can bespecified independent of the fast and slow states of the three pulleys20, 24, 26, the 24 state combinations can be specified from the othercombinations of the 54 combinations in total.

[0239] In actual engine tests, the difference combination (0, 0) occursmost frequency, because it corresponds to the combination of therespective normal states of the crank and cam pulleys 20, 24, 26.However, the combination (0, 0) also corresponds to the combination ofthe one-tooth fast state of the crank pulley 20 and the one-tooth slowstate of each of the left and right cam pulleys 24, 26 (i.e., (15+(−15),15+(−15))=(0, 0)) and the combination of the one-tooth slow state of thecrank pulley 20 and the one-tooth fast state of each of the left andright cam pulleys 24, 26 (i.e., (−15+15, −15+15)=(0, 0)). Thus, a personmight conclude that there are some cases where abnormal engines cannotbe identified from normal engines based on only the first test 1 usingthe difference Φ. However, in fact, the combination of the respectiveone-tooth fast states of the three pulleys 20, 24, 26, and thecombination of the respective one-tooth slow states of the three pulleys20, 24, 26 are technically the same as the state in which the threepulleys 20, 24, 26 are normal and only the timing belt 22 is one-toothslow or fast. Therefore, those state combinations do not adverselyaffect the operation of the engine 90.

[0240] Each of the state combinations corresponding to the differencecombination (0, 0) may be judged as being indicative of a normal engine,depending upon whether a similar test is carried out on the engine 90 ornot when it is partially taken apart and then re-assembled. For example,when one of the two cam pulleys 24, 26 is replaced with a new one in thecase where the three pulleys 20, 24, 26 are one-tooth fast, the new campulley will be normal but then the engine 90 as a whole will have faultswith the crank pulley and the other cam pulley. Thus, a person might notconsider it appropriate to judge each of the state combinationscorresponding to the difference combination (0, 0) as being indicativeof a normal engine. However, if the invention engine test is carried outagain on the engine 90 after it is partially taken apart andre-assembled, or an easier test is carried out on a specific section ofthe engine 90 which is actually taken apart and re-assembled and on asection or sections which is or are closely related to the specificsection, such faults as indicated above can be avoided. Therefore, inthe present embodiment, all the state combinations corresponding to thedifference combination (0, 0) are judged as being indicative of a normalengine.

[0241] If, at Step S802, the CPU identifies that the difference Φ[i]falls in the sixth range (6), it judges that the three pulleys 20, 24,26 are normal and the exhaust-valve clearance is normal. Therefore, theCPU does not make any additional judgments and quits the step. On theother hand, if the difference Φ[i] falls in the first range (1), the CPUsets, in the flag ‘flag_(crnk)’, 00×2 indicating that the crank pulley20 is one-tooth slow, sets, in the flag ‘flag_(cam)’, a value indicatingthat the left or right cam pulley 24, 26 is one-tooth fast (i.e., setsthe logical sum of 0×01 and the current value of the flag for the leftcam pulley 24, or sets the logical sum of 0×04 and the current value ofthe flag for the right cam pulley 26), and sets 1 to one of the bits ofthe flag ‘flag_(exs)’ which corresponds to the current content of thevariable ‘i’. Meanwhile, if the difference Φ[i] falls in the secondrange (2), the CPU performs the same operation as that performed in thecase where the difference Φ[i] falls in the first range (1), except forchanging the content of the flag ‘flag_(exs)’. In the case where thedifference Φ[i] falls in each of the third to tenth ranges (3) to (10),the CPU changes the respective contents of the corresponding faultflags. In the case where the difference Φ[i] falls in the eleventh range(11), the CPU sets 1 to the highest bit of each of the flags‘flag_(crnk)’, and ‘flag_(exs)’, thereby indicating that an error mayhave occurred. Based on the values 1 set in the respective highest bitsof those flags, the CPU may command the display 118 to indicate amessage requesting an operator to check the present engine testingapparatus. In the present embodiment, in the case where the differenceΦ[i] falls in the eleventh range (11), the CPU stops the current enginetesting operation and does not carry out any further steps for thetesting operation. Step S802 is followed by Step S804 to add 1 to thevariable ‘i’, and subsequently by Step S806 to judge whether the contentof the variable ‘i’ is equal to 6. If a positive judgment is made atStep S806, the control of the CPU quits the test 1. On the other hand,if a negative judgment is made, the control goes back to Step S802. Inthe test 1, whether the exhaust-valve clearance of each cylinder #1 to#6 is small or not can be judged clearly independent of the presence orabsence of other possible faults. In addition, there are some caseswhere the presence or absence of the fault with the assembling of eachof the crank pulley 20 and the cam pulleys 24, 26 can be identified.Based on the results obtained from the test 1, the CPU can judge whetherthe operation of the engine 90 is adversely influenced by the smallexhaust-valve clearance and/or the inappropriate assembling of the threepulleys 20, 24, 26.

[0242]FIG. 35 is a flow chart representing the test 2 called at StepS704 of FIG. 33. First, at Step S900, the CPU sets values in variables,A_(odd) and A_(even), respectively, based on the values obtained fromthe test 1 of FIG. 34. More specifically described, the CPU sets −30,−15, 0, 15, or 30 in the variable A_(odd) when the exhaust-pressuredecrease-start-angle difference Φ measured for the odd-numberedcylinders #1, #3, #5 of the left bank falls in the range (1) or (2), inthe range (3) or (4), in the range (5) or (6), in the range (7) or (8),and in the range (9) or (10), respectively. Similarly, the CPU sets anappropriate value in the variable A_(even). Step S900 is followed byStep S902 to initialize the variable ‘i’ to i=0, and subsequently byStep S904 to set, in a variable Δ, the value set in one of the variablesA_(odd) and A_(even) which corresponds to one of the two banks to whichthe current cylinder corresponding to the variable ‘i’ belongs. Inaddition, the CPU judges in which one of the following ranges (1) to(12) the value, Γ[i]−Δ, falls (Γ[i] is the exhaust-pressuremaximal-value-angle difference of the current cylinder):

[0243] Range (1): −30≦Γ[i]−Δ<−20

[0244] Range (2): −20≦Γ[i]−Δ<−16

[0245] Range (3): −16≦Γ[i]−Δ<−12

[0246] Range (4): −12≦Γ[i]−Δ<−6

[0247] Range (5): −6≦Γ[i]−Δ<−2

[0248] Range (6): −2≦Γ[i]−Δ<2

[0249] Range (7): 2≦Γ[i]−Δ<6

[0250] Range (8): 6≦Γ[i]−Δ<12

[0251] Range (9): 12≦Γ[i]−Δ<16

[0252] Range (10): 16≦Γ[i]−Δ<20

[0253] Range (11): 20≦Γ[i]−Δ<30

[0254] Range (12): Γ[i]−Δ<−30 or 30<Γ[i]−Δ

[0255] The reason why Step S904 is provided is that as is apparent fromFIG. 24, the difference Γ is produced only when the fast or slow stateof the driven gear 40, 42 or the large or small intake-valve clearanceoccurs, except for when the fast or slow state of the crank pulley 20,the left cam pulley 24, or the right cam pulley 26 occurs. Since thedifference Γ represents the sum of the respective influences of thefaults with the three pulleys 20, 24, 26, the fault with the driven gear40, 42, and the fault with the intake-valve clearance, the parameter,Γ−Δ, is free from the influences of the faults with the three pulleys20, 24, 26. The above-indicated eleven ranges (1) to (11) are determinedbased on the actual values of parameter (Γ−Δ) when the fault with thedriven gear 40, 42 and/or the fault with the intake-valve clearanceoccur or occurs. When the driven gear 40, 42 is one-tooth fast, normal,or one-tooth slow, the difference Γ stepwise changes to −18, 0, or 18,respectively. In the present embodiment, the fault finder 117 judges, ifthe difference Γ[i] of one cylinder falls in the range of −2 to 2, thatthe intake-valve clearance corresponding to the cylinder is normal.Therefore, even if the intake-valve clearance of one cylinder is judgedas normal, the difference Γ[i] of the cylinder may not be equal to 0 butmay take any value within the range of −2 to 2. In addition, thedifference Γ[i] of each cylinder cannot take a value smaller than −10 orgreater than 10, even if the intake-valve clearance of the cylinder isvery small or very great. FIG. 41 shows the eleven ranges (1) to (11) ofthe parameter (Γ−Δ) that are determined by taking the above-indicatedfacts into account. The eleven ranges (1) to (11) are defined by thefollowing twelve border values: −18±(10+2), −18±2, 0±(10+2), 0±2,18±(10+2), and 18±2. Each of the above twelve ranges (1) to (12)corresponds to the following faults of one of the two driven gears 40,42 which corresponds to the current cylinder, and the intake-valveclearance of the current cylinder:

[0256] Range (1): driven gear 40 or 42 one-tooth fast, and intake-valveclearance small

[0257] Range (2): driven gear 40 or 42 one-tooth fast, and intake-valveclearance normal

[0258] Range (3): driven gear 40 or 42 one-tooth fast, and intake-valveclearance large

[0259] Range (4): not specified

[0260] Range (5): driven gear 40 or 42 normal, and intake-valveclearance small

[0261] Range (6): driven gear 40 or 42 normal, and intake-valveclearance normal

[0262] Range (7): driven gear 40 or 42 normal, and intake-valveclearance large Range (8): not specified

[0263] Range (9): driven gear 40 or 42 one-tooth slow, and intake-valveclearance small

[0264] Range (10): driven gear 40 or 42 one-tooth slow, and intake-valveclearance normal

[0265] Range (11): driven gear 40 or 42 one-tooth slow, and intake-valveclearance large

[0266] Range (12): error

[0267] In the case where the difference Γ[i] falls in the sixth range(6), the control of the CPU directly goes to Step S912. In the casewhere the difference Γ[i] falls in one of the ranges (1) to (3), (5),(7), and (9) to (12), the control goes to Step S906. For example, if thedifference Γ[i] falls in the first range (1), the CPU sets, in the flag‘flag_(drvn)’, a value indicating that one of the driven gears 40, 42which corresponds to the current cylinder is one-tooth fast, and sets,in the flag ‘flag_(ins)’, a value indicating that the intake-valveclearance corresponding to the current cylinder is small. Morespecifically described, in the case where the variable ‘i’ is i=0, theCPU sets the logical sum of 0×04 and the current value of the flag‘flag_(drvn)’, in the flag ‘flag_(drvn)’, and sets the logical sum of0×01 and the current value of the flag ‘flag_(ins)’, in the flag‘flag_(ins)’. If the difference Γ[i] falls in each of the other ranges(2), (3), (5), (7), and (9) to (11), the CPU changes the respectivecontents of the corresponding fault flags. If the difference Γ[i] fallsin the range (12), the CPU performs the same operation as that performedwhen the exhaust-pressure decrease-start-angle difference Φ[i] falls inthe range (11) shown in FIG. 40, and stops the current engine testingoperation.

[0268] If the difference Γ[i] falls in the fourth range (4), the controlof the CPU goes to Step S908, i.e., test 2-1 as a subroutine. If thedifference Γ[i] falls in the eighth range (8), the control goes to StepS910, i.e., test 2-2 as a subroutine. Step S906, S908, or S910 isfollowed by Step S912 to add 1 to the variable ‘i’ and subsequently byStep S914 to judge whether the variable ‘i’ is equal to 6. If a positivejudgment is made at Step S806, the control of the CPU goes to Step S916and then quits the test 2. On the other hand, if a negative judgment ismade, the control goes back to Step S904. In the test 2, whether theassembling of the driven gears 40, 42 is normal or not and whether theintake-valve clearance of each cylinder #1 to #6 is normal or not can bejudged clearly independent of the presence or absence of other possiblefaults, except for the case where the difference Γ[i] falls in thetwelfth range (12). However, in the case where the difference Γ[i] fallsin the eighth range (8), the faults with the driven gears 40, 42 and theintake-valve clearance may not be identified from other possible faults,as will be described later.

[0269]FIG. 36 is a flow chart representing the test 2-1 called at StepS908 of FIG. 35. In the case where the difference Γ[i] falls in thefourth range (4), it is not possible to judge, based on the differenceΓ[i] only, whether the reason therefor is that the driven gear 40, 42 isone-tooth fast and the intake-valve clearance is large, or that theintake-valve clearance is small. Hence, this judgment is made based onother parameters. In the example shown in FIG. 36, the CPU calculatesthe sum of the exhaust-pressure decrease-start-angle difference Φ[i] andthe exhaust-pressure constant-start-angle difference Σ[i], andsubtracts, from the sum, double the variable obtained at Step S904. Theabsolute value of the thus obtained parameter (hereinafter, referred toas the “comparison parameter”) is employed for making the abovejudgment. The reason why the comparison parameter is employed is that asis apparent from FIG. 24, if the driven gear 40, 42 is one-tooth fastand the intake-valve clearance is large, the comparison parameter takes8.4 (=|−8.4+0|) and, if the intake-valve clearance is small, thecomparison parameter takes 0 (=|0+0|). For example, when the cam pulley24, 26 is one-tooth fast, the parameter (Φ[i]+Σ[i]) changes by −30(=−15−15) (i.e., decreases by 30) and, when the cam pulley 24, 26 isone-tooth slow, the parameter (Φ[i]+Σ[i]) changes by 30 (=15+15) (i.e.,increases by 30). When the crank pulley 20 is one-tooth fast and the campulley 24, 26 is one-tooth slow, the parameter (Φ[i]+Σ[i]) changes by60. However, since the comparison parameter is obtained by subtractingdouble the variable from the sum of the differences Φ[i], Σ[i], thecomparison parameter is free from the influences of possible faults withthe pulleys 20, 24, 26.

[0270] First, at Step S1000, the CPU judges whether the comparisonparameter (=|Φ[i]+Σ[i]−2·Δ|) is smaller than 4 that is about the averageof 8.4 and 0. If a positive judgment is made at Step S1000, the CPUjudges that the intake-valve clearance is small, and the control thereofgoes to Step S1002. On the other hand, if a negative judgment is made atStep S1000, the CPU judges that the driven gear 40, 42 is one-tooth fastand the intake-valve clearance is large, and the control thereof goes toStep S1004. The test 2-1 ends with Step S1002 or Step S1004. At StepS1002, the CPU sets 1 to one of the bits of the flag ‘flag_(ins)’ whichcorresponds to the current cylinder and, at Step S1004, the CPU sets 1to one of the bits of each of the flags ‘flag_(drvn)’ and ‘flag_(inl)’which corresponds to the current cylinder.

[0271]FIG. 37 is a flow chart representing the test 2-2 called at StepS910 of FIG. 35. In the case where the difference Γ[i] falls in theeighth range (8), it is not possible to judge, based on the differenceΓ[i] only, whether the reason therefor is that the intake-valveclearance is large, or that the intake-valve clearance is small. Hence,this subroutine is carried out as a preliminary operation before thetest 2-3, described later, in which the above judgment is made based onother information. Specifically described, at Step S1100, the CPU sets 1to one of the bits of the flag ‘flag_(inl)’ which corresponds to thecurrent cylinder and, at Step S1102, the CPU sets 1 to one of the bitsof the flag ‘flag_(ins)’ which corresponds to the current cylinder. Itis impossible that the intake-valve clearance is large andsimultaneously small. Therefore, 1 is set to one of the bits of each ofthe flags ‘flag_(inl)’, ‘flag_(ins)’ which corresponds to the currentcylinder, for just the purpose of indicating that the difference Γ[i]falls in the eighth range (8). The flags ‘flag_(inl)’, ‘flag_(ins)’ areutilized in the test 2-3 shown in FIG. 38 described below.

[0272]FIG. 38 is a flow chart representing the test 2-3 called at StepS916 of FIG. 35. According to this routine, in the case where thedifference Γ[i] of at least one cylinder falls in the eighth range (8),the CPU judges whether the reason therefor is that the driven gear 40,42 is one-tooth slow and the intake-valve clearance of the cylinder issmall, or that the intake-valve clearance of the cylinder is large,based on the parameters obtained from the other cylinders of one of thetwo banks to which the current cylinder belongs to. First, at StepS1200, the CPU initializes the variable ‘i’ to i=0 and, at Step S1202,judges whether the respective bits of the flags ‘flag_(inl)’,‘flag_(ins)’ which correspond to the current cylinder corresponding tothe variable ‘i’ are both 1. A positive judgment made at Step S1202indicates that the difference Γ[i] of the cylinder falls in the eighthrange (8). In this case, the control of the CPU goes to Step S1204 tojudge whether one of the driven gears 40, 42 which corresponds to one ofthe two banks which includes the cylinder indicated by the variable ‘i’is one-tooth slow. If a positive judgment is made at Step S1204, the CPUjudges that the intake-valve clearance of the current cylinder is small,because it is impossible that in the case where the difference Γ[i]falls in the range (8), the driven gear 40, 42 be one-tooth slow and theintake-valve clearance be large. In this case, Step S1204 is followed byStep S1206 to change 1 which has provisionally been set at Step S1100 ofFIG. 37 in one of the bits of the flag ‘flag_(inl)’ which corresponds tothe current cylinder, to 0 confirming that the intake-valve clearance issmall. Subsequently, Step S1206 is followed by Step S1208. On the otherhand, if a negative judgment is made at Step S1204, the control of theCPU directly goes to Step S1208. At Step S1208, the CPU add one to thevariable ‘i’ and, at Step S1210, the CPU judges whether the variable ‘i’is equal to 6. If a positive judgment is made at Step S1210, the CPUquits the test 2-3. On the other hand, if a negative judgment is made atStep S1210, the control goes back to Step S1202. In the case where anegative judgment is made at Step S1204, the CPU cannot specify whichfault has occurred to the cylinder whose difference Γ[i] falls in therange (8). In this case, the respective bits of the flags ‘flag_(inl)’,‘flag_(ins)’ which correspond to the current cylinder corresponding tothe variable ‘i’ are kept at 1, which may enable the CPU to inform theoperator of this situation.

[0273]FIG. 39 is a flow chart representing the test 3 called at StepS706 of FIG. 33. According to this routine, in the case where the tests1 and 2 show that the engine 90 is normal, the fault finder 117 can findthe large exhaust-valve clearance. However, in the case where the tests1 and 2 find a fault with at least one of the driven gear 40, 42 and theintake-valve clearance, the CPU judges that the large or normal state ofthe exhaust-valve clearance of one or more cylinders whose difference ordifferences B is or are influenced by that fault is not identifiable. Inaddition, in the case where the CPU judges that the exhaust-valveclearance of one cylinder is small when the test 2 ends, it is notpossible that the exhaust-valve clearance of that cylinder is large.Therefore, the CPU does not perform, at Step S1312 of FIG. 39, anyoperation on that cylinder. Only a compression-ring missing and a largeexhaust-valve clearance can influence the difference β of a cylinder,even if the difference β of the cylinder may not be influenced by anyfault with the driven gear 40, 42 or the intake-valve clearance of thecylinder. However, as can be understood from FIG. 24, the influence dueto the compression-ring missing is small. Therefore, if the difference βis not smaller than 7, the CPU can judge that the exhaust-valveclearance of that cylinder is large and, if not, judge that theexhaust-valve clearance is not large (i.e., small or normal). Thethreshold, 7, employed at Step S1304 is just an example like theabove-described thresholds.

[0274] At Step S1300, the CPU clears the variable ‘i’ to i=0 and, atStep S1302, the CPU judges whether the driven gear 40, 42 correspondingto the cylinder indicated by the variable ‘i’ and the intake-valveclearance of that cylinder are normal and simultaneously theexhaust-valve clearance of that cylinder is not small. If a positivejudgment is made at Step S1302, the control goes to Step S1304 to judgewhether the difference β[i] is not smaller than 7. If a positivejudgment is made at Step S1304, the CPU judges that the exhaust-valveclearance of that cylinder is large, and goes to Step S1306 to set 1 toone of the bits of the flag ‘flag_(exl)’ which corresponds to thatcylinder and then goes to Step S1308. On the other hand, if a negativejudgment is made at Step S1304, the CPU directly goes to Step S1308. Inthis case, the CPU judges that the exhaust-valve clearance of thatcylinder is normal. The test 3 is employed because this judgment can bemade. At Step S1308, the CPU adds one to the variable ‘i’ and, at StepS1310, the CPU judges whether the variable ‘i’ is equal to 6. If apositive judgment is made at Step S1310, the CPU quits the test 3. Onthe other hand, if a negative judgment is made at Step S1310, thecontrol goes back to Step S1302. If a negative judgment is made at StepS1302, the CPU judges that the large or normal state of theexhaust-valve clearance of the current cylinder is not identifiable. Inthis case, the control of the CPU goes to Step S1312 to set 1 to one ofthe bits of the flag ‘flag_(exl)’ which corresponds to the currentcylinder and set 1 to the highest bit of that flag and then goes to StepS1308. Thus, when the flag ‘flag_(exl)’ has 1 in the highest bitthereof, it indicates that the large or normal state of theexhaust-valve clearance of the cylinder corresponding to the bit of thatflag currently having 1 has not been identified or specified. However,as described previously, in the case where a negative judgment is madeat Step S1302 because the exhaust-valve clearance of a cylinder issmall, the CPU does not perform any operation at Step S1312.

[0275] In the present embodiment, in the case where the engine testingapparatus shows that the engine 90 does not have any faults except forthe fault of compression-ring missing, the CPU checks the presence orabsence of the fault on each of the cylinders, based on theexhaust-pressure maximal-value difference α of each cylinder. Althoughno flow chart is attached, if the engine 90 has no fault with the crankpulley 20, the cam pulleys 24, 26, or the driven gears 40, 42, theabsolute value of the difference β of a cylinder is smaller than, e.g.,3, and simultaneously the difference α of the cylinder is not greaterthan −5, the CPU judges that the cylinder has the fault of compression-ring missing, and sets 1 to one of the bits of the flag ‘flag_(ring)’which corresponds to the cylinder. However, the CPU does not change 0set in one of the bits of the flag which corresponds to a cylinder whosedifference α has changed due to the presence of another fault or otherfaults. In the case where the CPU finds such cylinder or cylinders, theCPU sets 1 to the highest bit of the flag ‘flag_(ring)’. When thehighest bit of the flag ‘flag_(ring)’ has 1, the cylinder correspondingto one of the bits of the flag which has 1 has the fault ofcompression-ring missing, but it has not been judged whether thecylinder corresponding to one of the bits of the flag which has 0 hasthe fault of compression-ring missing. The reason why the threshold, −5,is employed is that as is apparent from FIG. 24, the difference α takesa value about −10 when the compression-ring missing occurs. Thethreshold, −5, is about the average of 0 and −10. The reason why thedifference β is compared with 3 is that as is apparent from FIG. 24, inthe case where the engine 90 does not have any faults with the pulleys20, 24, 26 or the valves 48, 50, the absolute value of the difference βis smaller than 3.

[0276] It emerges from the foregoing description that in the secondembodiment of the present invention, the engine testing apparatus canspecify at least two faults out of a plurality of faults which may haveoccurred to an assembled engine 90. However, the testing apparatuscannot do so in all cases. For example, in the case where a cylinder hasthe missing of the compression ring and simultaneously the bankincluding that cylinder has the one-tooth fast state of the cam pulley24, 26, the testing apparatus does not judge whether the cylinder hasthe fault of compression-ring missing. However, for example, it ispossible to gather, in advance, information about, e.g., theexhaust-pressure maximal-value difference α of a cylinder when thecompression-ring missing and the one-tooth fast or slow state of the campulley 24, 26 simultaneously occur to the cylinder or the bank includingthe cylinder. In this case, the testing apparatus may judge whether thecylinder has the compression-ring missing even in the case where thecompression-ring missing and the one-tooth fast or slow state of the campulley 24, 26 simultaneously occur. Thus, the testing apparatus can testan assembled engine 90 based a on information other than that shown inFIG. 24.

[0277] Referring next to FIG. 42, there will be described a thirdembodiment of the present invention wherein an invention engine testingmethod is carried out by an engine testing apparatus shown in thefigure. In the present testing method, two exhaust manifolds 250 (onlyone 250 is shown) are attached to a left and a right bank of anassembled engine 90 to be tested, respectively. Each of the exhaustmanifolds 250 communicates with respective exhaust ports 100 of threecylinders of a corresponding one of the two banks, so that those exhaustports 100 communicate with a single exhaust pipe (not shown) via thatmanifold 250. A cover member 102 which is provided with a pressuresensor 106 is attached to an outlet of each exhaust manifold 250. Thus,the engine 90 has the same intake-valve side space 92, 94, 96 as shownin FIG. 4, and a pair of exhaust-valve side spaces each of which isprovided by respective inner spaces of a corresponding one of the twoexhaust manifolds 250 and the corresponding three exhaust ports 100.Since the present testing apparatus has one cover member 102 and onepressure sensor 106 for each bank, it enjoys a simpler construction thanthat shown in FIG. 4.

[0278]FIG. 43 shows respective exhaust-pressure signals P_(EX) obtainedfrom the left and right banks of the engine 90 by the testing apparatusshown in FIG. 42, together with a crank-shaft reference signal obtainedby the same. More specifically, FIG. 43 shows three pairs ofexhaust-pressure signals P_(EX) obtained when the engine 90 is normal,when the left cam pulley 24 is one-tooth fast, and when the pulley 24 isone-tooth slow, respectively. FIG. 44 illustrates, in a two- dimensionalcoordinate system and in an enlarged scale, the three exhaust-pressuresignals P_(EX) obtained from the left bank in the three cases shown inFIG. 43, respectively. FIG. 45 shows three pairs of exhaust-pressuresignals P_(EX) obtained when the engine 90 is normal, when the leftdriven gear 40 is one-tooth fast, and when the gear 40 is one-toothslow, respectively. FIG. 46 shows, in a two-dimensional coordinatesystem and in an enlarged scale, the three exhaust-pressure signalsP_(EX) obtained from the left bank in the three cases shown in FIG. 45,respectively. FIG. 47 shows a table including actual values of theexhaust-pressure maximal-value-angle difference Γ, the exhaust-pressureconstant-start-angle difference Σ, the exhaust-pressure maximal-valuedifference α, and the exhaust-pressure constant-value difference β whenthe left cam pulley 24 is one-tooth fast or slow or when the left drivegear 40 is one-tooth fast or slow. “Suffix 1” and “suffix 2” indicatedin the table of FIG. 47 correspond to the respective suffixed numbers ofthe symbols Γ, Σ, etc. indicated in the graphs of FIGS. 44 and 46.“Suffix 1” corresponds to the case where the pulley 24 or the gear 40 isone-tooth fast, and “suffix 2” corresponds to the case where the pulley24 or the gear 40 is one-tooth slow.

[0279] The comparison of FIG. 47 with FIG. 24 shows that the differencesΓ, Σ of FIG. 47 are equal to those of FIG. 24 but the differences α, βof FIG. 47 are smaller than those of FIG. 24. This is because the spaceshown in FIG. 42 from which the exhaust pressure P_(EX) is measured andthe table of FIG. 47 is obtained is larger than that shown in FIG. 4.That is, the latter space is provided by the respective spaces of eachcylinder and the corresponding exhaust port 100, whereas the formerspace is provided by the space of each manifold 250 in addition to therespective spaces of the corresponding three cylinders and thecorresponding three exhaust ports 100. Accordingly, the change ofpressure of the former space due to a certain event or fault is smallerthan that of the latter space due to the same cause. Although theexhaust-valve side space or volumes shown in FIG. 42 are larger thanthose shown in FIG. 4, the differences Γ, Σ of FIG. 47 are equal tothose of FIG. 24. This indicates that the simpler testing apparatus ofFIG. 42 can operate for finding the one-tooth fast or slow state of thedriven gear 40, 42 based on those differences Γ, Σ. The respectivechanges of the waveforms shown in FIG. 44 or FIG. 46 are producedbecause the respective timings of opening and closing of the intake andexhaust valves 50, 48 when the cam pulley 24, 26 or the driven gear 40,42 is one-tooth fast or slow differ from those when the engine 90 isnormal. Therefore, the engine testing apparatus of FIG. 42 can also findthe large or small state of the intake- or exhaust-valve clearance byanalyzing the changes of waveforms of FIG. 44 or FIG. 46 obtained fromthe engine 90. For example, the respective values of differences α, β,Γ, Σ indicated in the table of FIG. 47 stepwise change because of thefault with the cam pulley 24, 26 or the driven gear 40, 42. Therefore,if one of the differences α, β, Γ, Σ takes a value different from thoseindicated in the table of FIG. 47, the CPU of the present testingapparatus can judge that there is some possibility that the clearance ofan intake or an exhaust valve be not normal.

[0280] In each of the first to third embodiments, an intake-valve sidespace is provided by the respective inner spaces of the intake ports 92,the intake manifolds 94, and the surge tank 96. However, it is possiblethat an intake-valve side space be provided by only the inner space ofeach intake port 92. In this case, a pressure sensor 98 is provided foreach of the six intake-valve side spaces. That is, the respective intakepressures of the six cylinders are obtained independent of one another.Therefore, one or more faults with the assembling of an engine can befound based on one or more predetermined conditions of each of the sixintake pressures. Meanwhile, in each of the illustrated embodiments, theexhaust-valve side spaces are closed. However, the intake-valve sidespace or spaces may be closed in addition to, or in place of, theclosure of the exhaust-valve side spaces.

[0281] In the case where the six intake-valve side spaces are providedby the respective inner spaces of the intake ports 92 and each areclosed, the engine testing apparatus can obtain intake-pressuredifferences corresponding to the exhaust-pressure maximal-valuedifference α and the exhaust-pressure constant-value difference β andobtain angle differences corresponding to the exhaust-pressuredecrease-start angle Φ, etc., in the same manner as that employed forobtaining the table of FIG. 24. In this case, the assembled state of anengine can be checked based on those parameters.

[0282] In each of the illustrated embodiments, the V6 DOHC gasolineengines are tested. However, the present invention is applicable to thetesting of various types of engines. For example, in the case where SOHC(single over head cam shaft) engines are tested, the testing steps forfinding the fault with the driven gears 40, 42 are omitted. In addition,in the case where DOHC engines of the type wherein intake cam shafts(32, 34) are driven by not driven gears (40, 42) but different campulleys, testing steps for finding a fault with those different campulleys may be employed in place of the testing steps for finding thefault with the driven gears. Meanwhile, in each of the illustratedembodiments, the engine testing is carried out based on thecharacteristic parameter of the exhaust pressures P_(EX), such as theexhaust-pressure maximal value P_(EXmax) or the exhaust-pressuremaximal-value angle Θ_(EXmax). However, the other 152 parametersindicated in the table of FIG. 24 and/or the other characteristicparameters of the curves shown in the graphs of FIG. 8, FIG. 9, etc. maybe employed for the same purpose. For example, the maximum slope of thecurve shown in FIG. 8, or the crank-shaft angle corresponding to themaximum slope, the length and/or position of the interval in which therate of change of the curve is greater than a reference value, etc. maybe taken into account for finding a fault or faults with an assembledengine. The present invention may be also applicable to diesel engines.

[0283] In order to specify or identify, with higher reliability, each ofa plurality of faults which simultaneously occur to a single engine, theengine testing apparatus can gather more information from the engine.For example, all possible combinations of presence or absence ofpredetermined faults are artificially created on an engine, and thetesting apparatus gathers a group of respective values of predeterminedparameters P_(EXmax), Θ_(EXmax), etc. in each of all the combinations ofthe predetermined faults created on the engine. Then, the testingapparatus obtains a group of respective values of the predeterminedparameters P_(EXmax), Θ_(EXmax), etc. from an assembled engine, comparesthe obtained group of values with each of the groups of values gatheredin advance in all the fault combinations, and selects one of all thefault combinations as the specified or identified fault combination ofthe engine. In each of the illustrated embodiments, the testingapparatus finds the one-tooth fast or slow state of the crank pulley 20,the cam pulley 24, 26, or the driven gear 40, 42. However, the testingapparatus may be adapted to find the two or more teeth fast or slowstate of each pulley 20, 24, 26, 40, 42. In the last case, theparameters P_(EXmax), Θ_(EXmax), etc. may be classified in more stepsfor finding a fault or faults with high accuracy. In this case, theslight differences of respective values of each of those parameters mustbe distinguished from each other. Since the engine testing apparatusemployed in each of the illustrated embodiments can quickly obtain anumber of values of each of the parameters, it can find a fault orfaults with an engine with high reliability by, e.g., statisticallyanalyzing those values.

[0284] Next, there will be described a fourth embodiment of the presentinvention. The fourth embodiment is different from the above-describedfirst embodiment in that the engine testing routine of FIG. 25 employedin the first embodiment is replaced by a different engine testingroutine of FIG. 51 employed in the fourth embodiment. The engine testingapparatus of FIG. 4 employed in the first embodiment is also employed inthe fourth embodiment. However, in the fourth embodiment, the display118 of the control device 119 additionally includes six intake-valveforeign-matter-biting lamps 332 and six exhaust-valveforeign-matter-biting lamps 334, as shown in FIG. 52.

[0285] In the case where a foreign matter enters between each intakevalve 50 and a corresponding valve seat 74 and the intake valve 50 bitesthe foreign matter, in the case where the valve seat 74 is notappropriately set in the cylinder head 92 and has an inappropriateposture or position in the head 92, in the case where the intake valve50 is bent for some reason, or the like, the intake valve 50 cannot beappropriately seated on the valve seat 74 when the cam 46 is rotated(FIG. 3). Accordingly, the airtightness of the working volume of thecylinder cannot be maintained when it should be maintained. This is alsothe case with each exhaust valve 48. The above-indicated faults with theengine 90 may occur independent of the faults with the assembling of theengine 90. The following description relates to the fault offoreign-matter biting as a representative of the other faults that canbe specified or identified in the same manner.

[0286]FIG. 48 is a graph showing the change of exhaust pressure P_(EX)obtained from a cylinder of a normal engine and the change of exhaustpressure P_(EX) obtained from a cylinder of an engine having the faultof exhaust-valve foreign-matter biting. As is apparent from the graph,the latter exhaust pressure P_(EX) significantly changes in a periodcorresponding to the constant state (from the exhaust-pressureconstant-start angle Θ_(EXconst) to the exhaust-pressure decrease-startangle Θ_(EXdec)) of the former exhaust pressure P_(EX) obtained from thenormal engine. This is because, if the exhaust valve 48 of the cylinderbites a foreign matter, airtightness cannot be maintained between theexhaust port 100 and the working volume of the cylinder. Accordingly,the latter pressure P_(EX) in the exhaust port 100 is influenced andchanged by the pressure in the working volume of the cylinder, while thepressure P_(EX) would be constant if the valve 48 would be normal. Morespecifically described, the latter pressure P_(EX) increases in a periodin which the piston moves up toward its top dead position TDC, becausethe air compressed in the cylinder flows into the exhaust port 100.Subsequently, the latter pressure P_(EX) decreases in a period in whichthe piston moves down toward its bottom dead position BDC, because theworking volume of the cylinder increases and the high-pressure air inthe exhaust port 100 flows into the working volume.

[0287] In the above process, the latter pressure P_(EX) takes a maximalvalue, e.g., about 110 in the example shown in FIG. 48. This maximalvalue is greater by about 10% than the exhaust-pressure maximal valueP_(EXmax) (defined as 100) obtained from the normal engine. In addition,in the same process, the latter pressure P_(EX) takes a minimal value,e.g., about 0 in the example shown in FIG. 48. Thus, if the engine 90has the fault of exhaust-valve foreign-matter biting, the exhaustpressure P_(EX) obtained from the engine 90 changes between 0 and 110 inthe period corresponding the constant state of the exhaust pressureP_(EX) obtained from the normal engine. Since the exhaust-pressureconstant value P_(EXconst) obtained from the normal engine is constantat about 9, the exhaust-pressure constant-value difference β which wouldbe constant if the engine 90 would be normal changes between about −9and about 101.

[0288]FIG. 49 is a graph showing the change of exhaust pressure P_(EX)obtained from a cylinder of a normal engine and the change of exhaustpressure P_(EX) obtained from a cylinder of an engine having the faultof intake-valve foreign-matter biting. In the normal engine, theexhaust-pressure maximal-value angle Θ_(EXmax) that is a crank-shaft(CS) angle Θ_(crank) at which the exhaust pressure P_(EX) takes themaximal value P_(EXmax), is equal to a CS angle Θ_(INopen) at which theintake valve 50 opens (FIG. 6). However, in the engine having the faultof intake-valve foreign-matter biting, the exhaust pressure P_(EX) takesa maximal value P_(EXmax) at a CS angle smaller than the angleΘ_(INopen). Thus, the exhaust-pressure maximal-value-angle difference Γis about −26 in the example shown in FIG. 49. In the case where theengine has the fault of intake-valve foreign-matter biting, the exhaustport 100 keeps fluid communication with the respective inner spaces ofthe cylinder and the intake port 92, when the piston is around its topdead position TDC (FIG. 6) in the cylinder, that is, when the exhaustpressure P_(EX) is around the maximal value P_(EXmax)′. That is, the CSangle at which the exhaust pressure P_(EX) takes the maximal valueP_(EXmax)′ can change depending upon the respective pressures of theexhaust port 100, the working volume of the cylinder, and the intakeport 92.

[0289] In the case where the engine 90 has the fault of intake-valveforeign-matter biting but does not have the fault of exhaust-valveforeign-matter biting, the exhaust pressure P_(EX) takes a constantvalue P_(EXconst)′ in a period corresponding to the constant state ofthe exhaust pressure P_(EX) obtained from the normal engine. However,the constant value P_(EXconst)′ different from the constant valueP_(EXmax) obtained from the normal engine. This is because the workingvolume of the cylinder keeps fluid communication with the atmosphere viathe intake port 92. Accordingly, the pressure of the air compressed inthe cylinder is lower than that obtained from the normal engine, overthe substantially entire range of the CS angle. That is, the maximalvalue P_(EXmax)′ is smaller than the maximal value P_(EXmax) obtainedfrom the normal engine. In the example shown in FIG. 49, the maximalvalue P_(EXmax)′ and the constant value P_(EXconst)′ are about 21 andabout 0, respectively, and the differences α, β are about −79 and about−9, respectively.

[0290] In the case where the engine 90 has the fault of intake-valveforeign-matter biting, the CS angle at which the exhaust pressure P_(EX)starts taking the constant value P_(EXconst)′ is smaller than thatobtained from the normal engine. In the normal engine, this CS angle isequal to the angle at which the exhaust valve 48 starts closing.However, in the engine 90 having the fault, the respective pressures ofthe intake port 92, the exhaust port 100, and the working volume of thecylinder are balanced by one another earlier than in the normal engine,because the pressure in the cylinder is lower than that in the normalengine. Thus, the exhaust-pressure constant-start-angle difference Σtake a negative value, e.g., about −18 in the example shown in FIG. 49.The constant value P_(EXconst)′ is about 0 (in terms of gauge pressure),i.e., substantially equal to the atmospheric pressure.

[0291]FIG. 50 shows a table which is different from the table shown inFIG. 24 in that the former table additionally includes respective actualvalues of the exhaust-pressure maximal-value difference α, theexhaust-pressure constant-value difference β, the exhaust-pressuremaximal-value-angle difference Γ, the exhaust-pressureconstant-start-angle difference Σ, etc. which are obtained in the casewhere the fault of intake-valve or exhaust-valve foreign-matter bitingoccurs to the engine 90 independent of the other faults.

[0292] In the fourth embodiment, the engine 90 is tested mainlydepending upon amounts relating to the exhaust-pressure constant-valuedifference β. Next, the fourth engine testing method in accordance withthe present invention will be described.

[0293]FIG. 51 is a flow chart representing the main routine of an enginetesting program which is employed in the fourth embodiment, in place ofthe main routine of FIG. 25 employed in the first embodiment. Thepresent testing program is pre-stored in the ROM of the fault finder 117and which is carried out by the CPU and the RAM of the finder 117.According to the main routine, the fault finder 117 identifies thepresence or absence of a fault of the engine 90. If the engine 90 has nofault, the finder 117 commands the display 118 shown in FIG. 52 toindicate that the engine 90 has passed the test. On the other hand, if afault is found, the finder 117 identifies or specifies what is thefault, and then commands the display 118 to indicate that the engine 90has not passed the test and additionally indicate what is the fault. Inthe present testing program, it is assumed that only a single faultoccurs, if any, that is, two or more faults do not simultaneously occur.

[0294] First, at Step T100, the fault finder 117 or the CPU thereofjudges whether respective values of the exhaust-pressure maximal-valuedifference α, the exhaust-pressure constant-value difference β, theexhaust-pressure maximal-value-angle difference Γ, the exhaust-pressureconstant-start-angle difference Σ, the exhaust-pressuredecrease-start-angle difference Φ, the intake-pressuremaximal-value-angle difference Λ, and the intake-pressureincrease-start-angle difference Ψ which are measured from each one ofthe six cylinders #1 to #6 of the engine 90 fall in seven referenceranges, respectively. For example, a standard deviation, σ, of each ofthe seven differences indicated in the table is obtained from aplurality of normal engines (e.g., 1,000 engines), and the referencerange therefor is determined as 0±3σ. The seven reference ranges whichmay differ from one another will be expressed as α_(TH), β_(TH), Γ_(TH),Σ_(TH), Φ_(TH), Λ_(TH), Ψ_(TH), respectively. When the assembling of theengine 90 is normal, the difference α, for example, falls in the rangeof 0±α_(TH), that is, the conditional expression: 0−α_(TH)≦α≦0+α_(TH) istrue. Therefore, if the respective conditional expressions for the sevendifferences are all true, a positive judgment is made at Step T100 andthe control of the CPU goes to Step T102 to command the display 118 tolight the OK lamp 200 indicating that no fault has been found and theengine 90 has passed the test. Subsequently, the CPU quits the mainroutine. On the other hand, if a negative judgment is made at Step T100,that is, a fault has been found, the control goes to Step T104 to lightthe NG lamp 202 indicating this situation and that the engine 90 has notpassed the test. Subsequently, the control of the CPU goes to Step T106,i.e., a fault identifying or specifying subroutine. Step T106 isfollowed by Step T108 to light a lamp of the display 118 correspondingto the fault specified at Step T106. Then, the CPU quits the mainroutine.

[0295] As indicated above, in the present engine testing method, theamounts relating to the exhaust-pressure constant-value difference β,that is, the difference β itself, the exhaust-pressuredecrease-start-angle difference Φ, and the exhaust-pressureconstant-start-angle difference Σ are mainly utilized for finding eachof various faults with the assembling of the engine 90. However, othersorts of differences may be employed. For example, all the sevendifferences are utilized at Step T100.

[0296]FIG. 53 is a flow chart representing the fault specifyingsubroutine of Step T106 of FIG. 51. In the present subroutine, first, atStep T200, the CPU of the fault finder 117 initializes, to 0×00, each often fault flags corresponding to the faults indicated in the table ofFIG. 50. In the present embodiment, the RAM of the fault finder 117 hasthe same fault flags as those employed in the first embodiment and shownin FIG. 28, and additionally has two fault flags, ‘flag_(ina)’ and‘flag_(exa)’, corresponding to the intake-valve and exhaust-valveforeign-matter biting, respectively. As shown in FIG. 54, each of thosetwo flags also comprises one byte data, i.e., eight bits data. If nofault has been found, each flag remains 0×00. The lower six bits of theflag ‘flag_(ina)’ represent the presence or absence of the intake-valveforeign-matter biting of the cylinders #1 to #6 of the engine 90,respectively, and the lower six bits of the flag ‘flag_(exa)’ representthe presence or absence of the exhaust-valve foreign-matter biting ofthe cylinders #1 to #6, respectively. The respective highest (left-end)bits of those two flags are doubtful-fault bits each of which may be setto 1 to indicate that a corresponding fault is doubtful but cannot beidentified.

[0297] Step T200 is followed by Steps T202 to T226. Step T202 is acrank-pulley test for determining values to be set to the flag‘flag_(crnk)’. Steps T206 is a cam-pulley test for determining values tobe set to the flag ‘flag_(cam)’. Step T210 is a driven-gear test fordetermining values to be set to the flag ‘flag_(drvn)’, Step T214 is aforeign-matter-biting test for determining values to be set to the flags‘flag_(ina)’, ‘flag_(exa)’. Step T218 is a valve-clearance test fordetermining values to be set to the flags ‘flag_(ins)’, ‘flag_(inl)’,‘flag_(exs)′, ‘flag_(exl)′’. Step T222 is a compression-ring test fordetermining values to be set to the flag ‘flag_(ring)’. If a fault isfound at any of those steps, that is, if a negative judgment is made atany of Steps T204, T208, T212, T216, T220, and T224, then the CPUimmediately quits the fault specifying routine and the remaining stepsare not carried out. This manner corresponds to the above-indicatedassumption that only a single fault occurs to a single engine 90. If apositive judgment is made at each of Steps T204, T208, T212, T216, T220,and T224, then the control of the CPU goes to Step T226 which will bedescribed later. Thereafter, the CPU quits the present subroutine.

[0298] First, the crank-pulley test at Step T202 of FIG. 53 will bedescribed below.

[0299]FIG. 55 is a flow chart representing the crank-pulley testingsubroutine of Step T202 of FIG. 53. First, at Step T300, the CPU of thefault finder 117 judges whether a variable, J1_(i), corresponding to thecurrent cylinder indicated by the content of a variable ‘i’ is 1. Thevariable J1_(i) is defined by the following logical expression:

J1_(i)=(−β_(TH≦β) _(i)≦β_(TH)) ∩ (15−Σ_(TH)≦Σ_(i)≦15+Σ_(TH)) ∩(15−Φ_(TH) ≦Φ _(i)≦15+Φ_(TH))  (1)

[0300] The variable ‘J1_(i)’ takes 1 corresponding to TRUE when theabove expression is correct, or 0 corresponding to FALSE when theexpression is not correct. If the variable J1_(i) corresponding to everycylinder #1 to #6 is 1 (i.e., TRUE), the control of the CPU goes to StepT302 to set, in the fault flag ‘flag_(crnk)’ 0×01 indicating that thecrank pulley is one-tooth fast. Then, the CPU quits the presentsubroutine. On the other hand, if the variable J1_(i) corresponding toat least one cylinder #1 to #6 is 0 (i.e., FALSE), the control goes toStep T304 to judge whether a variable, J2_(i), corresponding to thecurrent cylinder indicated by the variable ‘i’ is 1. The variable J₂_(i) is defined by the following logical expression:

J2_(i)=(−β_(TH)≦β_(i)≦β_(TH)) ∩ (−15−Σ_(TH)≦Σ_(i)≦−15+Σ_(TH)) ∩(−15−Φ_(TH)≦Φ_(i)≦−15+Φ_(TH))  (2)

[0301] If the variable J2_(i) corresponding to every cylinder #1 to #6is 1 (TRUE), the control goes to Step T306 to set, in the flag‘flag_(crnk)’, 0×02 indicating that the crank pulley is one-tooth slow.Then, the CPU quits the subroutine. On the other hand, if the variableJ2_(i) corresponding to at least one cylinder #1 to #6 is 0 (FALSE), theCPU directly quits the subroutine.

[0302] A negative judgment made at Step T304 indicates that the crankpulley 18 is normal. In this case only, the content of the flag‘flag_(crnk)’ remains 0×00 as it was initialized at Step T200 of FIG.53, and a positive judgment is made at Step T204. Then, the control goesto Step T206.

[0303]FIG. 56 is a flow chart representing the cam-pulley testingsubroutine of Step T206 of FIG. 53. First, at Step T400, the CPU judgeswhether the variable J2_(i) corresponding to every cylinder #1, #3, #5of the left bank is 1 (TRUE). Hereinafter, the variable J2_(i) for theodd-numbered cylinders #1, #3, #5 of the left bank will be referred toas the variable J2_(odd). The suffix “odd” indicates that the content ofthe variable ‘i’ is an odd number. If a positive judgment is made atStep T400, the control of the CPU goes to Step T402 to set, in the faultflag ‘flag_(cam)’, 0×01 indicating that the left cam pulley 24 isone-tooth fast. Then, the CPU quits the present subroutine. On the otherhand, if the variable J2_(odd) corresponding to at least one cylinder#1, #3, #5 is 0 (FALSE), the control goes to Step T404 to judge whetherthe variable J1_(i) corresponding to every cylinder #1, #3, #5 of theleft bank is 1 (TRUE). Hereinafter, the variable J1_(i) for theodd-numbered cylinders #1, #3, #5 of the left bank will be referred toas the variable J1_(odd). If a positive judgment is made at Step T404,the control of the CPU goes to Step T406 to set, in the flag‘flag_(cam)’, 0×02 indicating that the left cam pulley 24 is one-toothslow. Then, the CPU quits the subroutine. On the other hand, if thevariable J1_(odd) corresponding to at least one cylinder #1, #3, #5 is 0(FALSE), the control goes to Step T408 to judge whether the variableJ2_(i) corresponding to every cylinder #2, #4, #6 of the right bank is 1(TRUE). Hereinafter, the variable J2_(i) for the even-numbered cylinders#2, #4, #6 of the right bank will be referred to as the variableJ2_(even). The suffix “even” indicates that the content of the variable‘i’ is an even number. If a positive judgment is made at Step T408, thecontrol of the CPU goes to Step T410 to set, in the flag ‘flag_(cam)’,0×04 indicating that the right cam pulley 26 is one-tooth fast. Then,the CPU quits the subroutine. On the other hand, if the variableJ2_(even) corresponding to at least one cylinder #2, #4, #6 is 0(FALSE), the control goes to Step T412 to judge whether the variableJ1_(i) corresponding to every cylinder #2, #4, #6 of the right bank is 1(TRUE). Hereinafter, the variable J1_(i) for the even-numbered cylinders#2, #4, #6 of the right bank will be referred to as the variableJ1_(even). If a positive judgment is made at Step T412, the control ofthe CPU goes to Step T414 to set, in the flag ‘flag_(cam)’, 0×08indicating that the right cam pulley 26 is one-tooth slow. Then, the CPUquits the subroutine. On the other hand, if the variable J1_(even)corresponding to at least one cylinder #2, #4, #6 is 0 (FALSE), the CPUdirectly quits the subroutine. A negative judgment made at Step T412indicates that the two cam pulleys 24, 26 are normal. In this case only,the content of the flag ‘flag_(cam)’ remains 0×00 as it was initializedat Step T200 of FIG. 53, and a positive judgment is made at Step T208.Then, the control goes to Step T210.

[0304]FIG. 57 is a flow chart representing the driven-gear testingsubroutine of Step T210 of FIG. 53. First, at Step T500, the CPU judgeswhether a variable, J3_(i) (expressed as J3_(odd)), corresponding toevery cylinder #1, #3, #5 of the left bank is 1 (TRUE). The variableJ3_(i) is defined by the following logical expression:

J3_(i)=(−10−β_(TH)≦β_(i)≦−10+β_(TH)) ∩ (−8.4−Σ_(TH)≦Σ_(i)≦−8.4+ρ_(TH)) ∩(−Φ_(TH)≦Φ_(i)≦Φ_(TH))  (3)

[0305] If a positive judgment is made at Step T500, the control of theCPU goes to Step T502 to set, in the fault flag ‘flag_(drvf)’, 0×01indicating that the left driven gear 40 is one-tooth fast. Then, the CPUquits the present subroutine. On the other hand, if a negative judgmentis made at Step S500, the control goes to Step T504 to judge whether avariable, J4_(i) (expressed as J4_(odd)) corresponding to every cylinder#1, #3, #5 of the left bank is 1 (TRUE). The variable J4_(i) is definedby the following logical expression:

J4_(i)=(36−β_(TH)≦β_(i)≦36+β_(TH)) ∩ (−ρ_(TH)≦ρ_(i)≦ρ_(TH)) ∩(−Φ_(TH)≦Φ_(i)≦Φ_(TH))  (4)

[0306] If a positive judgment is made at Step T504, the control of theCPU goes to Step T506 to set, in the flag ‘flag_(drvn)’, 0×02 indicatingthat the left driven gear 40 is one-tooth slow. Then, the CPU quits thesubroutine. On the other hand, if a negative judgment is made at StepS504, the control goes to Step T508 to judge whether the variable J3_(i)(J3_(even)) corresponding to every cylinder #2, #4, #6 of the right bankis 1 (TRUE). If a positive judgment is made at Step T508, the control ofthe CPU goes to Step T510 to set, in the flag ‘flag_(drvn)’, 0×04indicating that the right driven gear 42 is one-tooth fast. Then, theCPU quits the subroutine. On the other hand, if a negative judgment ismade at Step S508, the control goes to Step T512 to judge whether thevariable J4_(i) (J4_(even)) corresponding to every cylinder #2, #4, #6of the right bank is 1 (TRUE). If a positive judgment is made at StepT512, the control of the CPU goes to Step T514 to set, in the flag‘flag_(drvn)’, 0×08 indicating that the right driven gear 42 isone-tooth slow. Then, the CPU quits the subroutine. On the other hand,if a negative judgment is made at Step T512, the CPU directly quits thesubroutine. A negative judgment made at Step T512 indicates that the twodriven gears 40, 42 are normal. In this case only, the content of theflag ‘flag_(drvn)’ remains 0×00 as it was initialized at Step T200 ofFIG. 53, and a positive judgment is made at Step T212. Then, the controlgoes to Step T214.

[0307]FIG. 58 is a flow chart representing the foreign-matter-bitingtesting subroutine called at Step T214 of FIG. 53. First, at Step T600,the CPU sets 0×01 to a variable ‘buf’ and, at Step T602, the CPUinitializes the variable ‘i’ to 0 corresponding to the first piston orcylinder #1. Subsequently, at Step T604, the CPU judges whether avariable, J5_(i), corresponding to the current cylinder is 1 (TRUE). Thevariable J5_(i) is defined by the following logical expression:

J5_(i)=(MAXβ_(TH)<MAX(β_(i))) ∩ (−Σ_(TH)≦ρ_(i)≦ρ_(TH)) ∩(−Φ_(TH)≦Φ_(i)≦Φ_(TH))  (5)

[0308] MAX(β_(i)) is a function which provides the maximum value of thevariable exhaust-pressure constant-value difference β_(i) (FIG. 48), andMAXβ_(TH) is a threshold value. In the present embodiment, the thresholdvalue is selected at 60. However, any value that permits the CPU to makea reliable judgment at Step T604 may be selected as the threshold value.For example, the average value B obtained from normal engines plus 3σmay be employed as the threshold value. That the difference β_(i) isgreater than the threshold value MAXβ_(TH) is one condition for judgingthat the foreign-matter biting has occurred. A positive judgment made atStep T504 indicates that the foreign-matter biting has occurred to theexhaust valve or valves 48 of the current cylinder indicated by thevariable ‘i’. In this case, the control of the CPU goes to Step T606 toset the logical sum of the flag ‘flag_(exa)’ and the variable ‘buf’,again to the flag ‘flag_(exa)’. Consequently one of the lower six bitsof the flag ‘flag_(exa)’ which corresponds to the current cylinder ischanged to 1 indicating that the fault has occurred to that cylinder.

[0309] On the other hand, if a negative judgment is made at Step T604,the control goes to Step T608 to judge whether a variable, J6_(i),corresponding to the current cylinder is 1 (TRUE). The variable J6_(i)is defined by the following logical expression:

J6_(i)=(β_(i)<−β_(TH)) ∩ (Σ_(i)≦−Σ_(TH)) ∩ (−Φ_(TH)≦Φ_(i)≦Φ_(TH))   (6)

[0310] A positive judgment made at Step T608 indicates that theforeign-matter biting has occurred to the intake valve or valves 50 ofthe current cylinder indicated by the variable ‘i’. In this case, thecontrol goes to Step T610 to set the logical sum of the content of thevariable ‘buf’ and the content of the flag ‘flag_(ina)’, again in theflag ‘flag_(ina)’. On the other hand, if a negative judgment is made atStep T608, the control goes to Step T612, which also follows Step T606or Step T610. At Step T612, the CPU adds one to the content of thevariable ‘i’. Step T612 is followed by Step T614 to judge whether thecontent of the variable ‘i’ is equal to 6. If a positive judgment ismade at Step T614, the CPU quits the present subroutine. On the otherhand, if a negative judgment is made, the control goes to Step T616 toshift 1 from the current bit to the next, higher bit in the variable‘buf’, so that the number (0, 1, 2, 3, 4, or 5) allotted to the bithaving 1 coincides with the number indicated by the content of thevariable ‘i’. Then, the control of the CPU goes back to Step T604. Thevalue ‘1’ set in a bit of the flag ‘flag_(exa)’ or ‘flag_(ina)’indicates that a fault has occurred to the cylinder corresponding tothat bit.

[0311]FIG. 59 is a flow chart representing the valve-clearance testingsubroutine called at Step T218 of FIG. 53. First, at Step T700, the CPUsets 0×01 to the variable ‘buf’ and, at Step T702, the CPU initializesthe variable ‘i’ to 0 corresponding to the first piston or cylinder #1.Subsequently, at Steps T704, T708, T712, and T716, the CPU judgeswhether the small or large state of the intake-valve or exhaust-valveclearance has occurred to the current cylinder, by utilizing fourvariables J7_(i), J8_(i), J9_(i), and J10_(i) defined by the followingfour logical expressions, respectively:

J7_(i)=(β_(i)<−β_(TH)) ∩ (Γ_(i)<−Γ_(TH)) ∩ (−ρ_(TH)≦ρ_(i)≦Σ_(TH)) ∩(−Φ_(TH)≦Φ_(i)≦Φ_(TH))  (7)

J8_(i)=(β_(TH)<β_(i)) ∩ (−Σ_(TH)≦Σ_(TH)≦Σ_(i)≦Σ_(TH)) ∩(−Φ_(TH)≦Φ_(i)≦Φ_(TH)) ∩ (Γ_(TH)<Γ_(i))  (8)

J9_(i)=(β_(i)<−β_(TH)) ∩ (Σ_(TH)<Σ_(i)) ∩ (Φ_(i)<−Φ_(TH))  (9)

J10_(i)=(β_(TH)<β_(i)) ∩ (−Σ_(TH)≦Σ_(i)Σ_(TH)) ∩ (−Φ_(TH)≦Φ_(i)≦Φ_(TH))∩ (−Γ_(TH)≦Γ_(i)≦Γ_(TH))  (10)

[0312] In each of the expressions (8) and (10), the exhaust-pressuremaximal-value-angle difference Γ_(i) is taken into account, because asis apparent from the table shown in FIG. 50, the respective large statesof the intake-valve and exhaust-valve clearances cannot be distinguishedfrom each other based on only the exhaust-pressure constant-valuedifference β_(i), the exhaust-pressure constant-start-angle differenceΣ_(i), and the exhaust-pressure decrease-start-angle difference Φ_(i).The difference Γ_(i) is also taken into account, because as is apparentfrom FIG. 50 the compression-ring missing (the test therefor will bedescribed later by reference to FIG. 60) and the small state of theintake-valve clearance cannot be distinguished from each other based ononly those differences.

[0313] If it is judged that the variable J7_(i) is 1 (TRUE), that is, ifa positive judgment is made at Step T704, the control of the CPU goes toStep T706 to set the logical sum of the content of the variable ‘buf’and the content of the fault flag ‘flag_(ins)’, again in the flag‘flag_(ins)’. If it is judged at Step T708 that the variable J8_(i) is 1(TRUE), the control of the CPU goes to Step T710 to set the logical sumof the content of the variable ‘buf’ and the content of the flag‘flag_(inl)’, again in the fault flag ‘flag_(inl)’. If it is judged atStep T712 that the variable J9_(i) is 1 (TRUE), the control of the CPUgoes to Step T714 to set the logical sum of the content of the variable‘buf’ and the content of the fault flag ‘flag_(exs)’, again in the flag‘flag_(exs)’. If it is judged at Step T716 that the variable J10_(i) is1 (TRUE), the control of the CPU goes to Step T718 to set the logicalsum of the content of the variable ‘buf’ and the content of the faultflag ‘flag_(exl)’, again in the flag ‘flag_(exl)’. At Step T720, one isadded to the variable ‘i’ and, at Step T722, the CPU judges whether thecontent of the variable ‘i’ is equal to 6. If a positive judgment ismade at Step T722, the CPU quits the subroutine. On the other hand, if anegative judgment is made, the control goes to Step T724 to shift 1 fromthe current bit to the next, higher bit in the variable ‘buf’, so thatthe number allotted to the bit having 1 coincides with the numberindicated by the content of the variable ‘i’ incremented at Step T720.Then, the control of the CPU goes back to Step T704.

[0314]FIG. 60 is a flow chart representing the compression-ring testingsubroutine called at Step T222 of FIG. 53. First, at Step T800, the CPUsets 0×01 to the variable ‘buf’ and, at Step T802, the CPU initializesthe variable ‘i’ to 0 corresponding to the first piston or cylinder #1.Subsequently, at Step T804, the CPU judges whether a variable, J11_(i),corresponding to the current cylinder is 1 (TRUE). The variable J11_(i)is defined by the following logical expression:

J11_(i)=(β_(i)≦β_(TH)) ∩ (−Γ_(TH)≦Γ_(i)≦Γ_(TH)) ∩ (−Σ_(TH)≦Σ_(i)≦Σ_(TH))∩ (−Φ_(TH)≦Φ_(i)≦Φ_(TH))  (11)

[0315] In the logical expression (11), the exhaust-pressuremaximal-value-angle difference Γ_(i) is taken into account, so that thecompression-ring missing may be distinguished from the small state ofthe intake-valve clearance. However, in the present subroutine, theconditional expression relating to the difference Γ_(i) may be omittedfrom the logical expression (11), because the difference Γ_(i) has beentaken into account at Step T218, i.e., the valve-clearance test fordistinguishing the fault of small intake-valve clearance from the faultof compression-ring missing. A positive judgment made at Step T804indicates that the compression-ring missing has occurred to the pistonof the current cylinder. In this case, the control of the CPU goes toStep T806 to set the logical sum of the content of the variable ‘buf’and the content of the fault flag ‘flag_(ring)’, again in the flag‘flag_(ring)’. At Step T808, one is added to the variable ‘i’ and, atStep T810, the CPU judges whether the content of the variable ‘i’ isequal to 6. If a positive judgment is made at Step T810, the CPU quitsthe subroutine. On the other hand, if a negative judgment is made, thecontrol goes to Step T812 to shift 1 from the current bit to the next,higher bit in the variable ‘buf’. Then, the control of the CPU goes backto Step T804.

[0316] Step T224 is followed by Step T226, i.e., a complementary step.Only in the case where no fault has been specified or identified atSteps T200 to T224 of the fault specifying subroutine of FIG. 53, thecontrol of the CPU reaches this step. However, the subroutine of FIG. 53is called when the main routine of FIG. 51 shows that there ispossibility that some fault has occurred to the engine 90. That is, thefact that the CPU reaches Step T226 indicates that the test resultobtained from the routine of FIG. 53 is not compatible with thatobtained from the routine of FIG. 51. However, the CPU cannot know thereason therefor. Accordingly, the CPU sets 1 to the highest bit of everyfault flag, so that the lamps corresponding to all the fault flags flashon the display 118. Thus, the fault finder 117 can prevent itself fromerroneously judging that the engine 90 is a normal engine,notwithstanding the presence of incompatibility of the test results.

[0317] Referring next to FIG. 61, there will be described a fifthembodiment of the present invention wherein an invention engine testingmethod is carried out by an engine testing apparatus shown in thefigure. The testing apparatus shown in FIG. 61 is basically similar tothe apparatus shown in FIG. 4. The same reference numerals as used inFIG. 4 are used to designate the corresponding elements and parts of theapparatus shown in FIG. 61, and the description of those elements andparts is omitted. In the present testing method, a generally tubularsupport member 450 is fixed to each of the six exhaust ports 100. TwoO-shaped rings 104 are attached to opposite end faces of the supportmember 450 to maintain airtightness. One of the two end faces of thesupport member 450 is held in close contact with the exhaust port 100. Acover member 102 is attached to the other end face of the support member450. When the cover member 102 is closed or opened, the exhaust-valveside space (i.e., respective inner spaces of the exhaust port 100 andthe support member 450) is closed or opened. FIG. 61 shows the covermember 102 in its opened state. With the cover member 102 being closed,the respective inner spaces of the exhaust port 100 and the supportmember 450 are isolated from the atmosphere. A pressure sensor 106 isattached to each of the six support members 450, at a position where thesensor 106 can measure the pressure in the inner space of each supportmember 450. Thus, the pressure sensor 106 can measure the pressure inthe exhaust-valve side space both when the space is its closed state andwhen the space is in its opened state. A similar arrangement is providedfor each of the intake ports 92. More specifically described, agenerally tubular support member 454 is fixed to each of the six intakeports 92. Two O-shaped rings 104 are attached to opposite end faces ofthe support member 454 to maintain airtightness. One of the two endfaces of the support member 454 is held in close contact with the intakeport 92. A cover member 458 is attached to the other end face of thesupport member 454. When the cover member 458 is closed or opened, theintake-valve side space (i.e., respective inner spaces of the intakeport 92 and the support member 454) is closed or opened. FIG. 61 showsthe cover member 458 in its closed state. With the cover member 458being closed, the respective inner spaces of the intake port 92 and thesupport member 454 are isolated from the atmosphere. A pressure sensor98 is attached to each of the six support members 454, at a positionwhere the sensor 98 can measure the pressure in the inner space of eachsupport member 454. Thus, the pressure sensor 98 can measure thepressure in the intake-valve side space both when the space is itsclosed state and when the space is in its opened state. Each of thecover members 102, 458 is switched between its closed and opened statesby a drive device (not shown) under control of the control device 119.

[0318] Thus, the cover members 102 can be closed and opened independentof the closing and opening of the cover members 458. In the presentembodiment, two covering manners are utilized for testing an engine 90,as will be described below: in the first covering manner, the covermembers 102 are opened and the cover members 458 are closed and, in thesecond covering manner, vice versa. It is possible that an engine testbe carried out in a manner in which all the cover members 102, 458 areopened, or in a manner in which all the cover members 102, 458 areclosed. However, since those manners are just employed for very specificpurposes, the detailed description thereof is omitted.

[0319] The first covering manner is similar to the covering manneremployed in the fourth embodiment of the invention engine testingmethod, since the exhaust-valve side space is closed and theintake-valve side space is opened. Therefore, the results similar tothose shown in FIG. 50 (i.e., the exhaust-pressure maximal-valuedifference α, the exhaust-pressure constant-value difference β, theexhaust-pressure maximal-value-angle difference Γ, the exhaust-pressureconstant-start-angle difference Σ, and the exhaust-pressuredecrease-start-angle difference Φ) are obtained based on the exhaustpressures P_(EX) measured in the first covering manner. Although in thefourth embodiment the intake manifolds 94 are employed like the firstembodiment shown in FIG. 4, no intake manifold is employed in thepresent, fifth embodiment. This causes differences of the respectiveexhaust pressures P_(EX) obtained from the two embodiments. However,those differences are small. Hereinafter, the differences α, β, Γ, Σ, Φobtained in the first covering manner will be indicated by symbolsα_(EX), β_(EX), θ_(EX), Σ_(EX), Φ_(EX), respectively.

[0320] In the second covering manner, the drive motor 125 is rotated inthe opposite direction, so that the crank shaft 18 is rotated in thedirection opposite to the normal direction in which the crank shaft 18is rotated when the engine 90 is actually operated by firing.Accordingly, the respective intake pressures P_(IN) measured by the sixpressure sensors 98 change like the respective exhaust pressures P_(EX)measured by the six pressure sensors 106 in the first covering manner.Thus, the control device 119 obtains, from each cylinder, anexhaust-pressure maximal-value difference α_(IN), an exhaust-pressureconstant-value difference β_(IN), an exhaust-pressuremaximal-value-angle difference Γ_(IN), an exhaust-pressureconstant-start-angle difference Σ_(IN), and an exhaust-pressuredecrease-start-angle difference Φ_(IN) which correspond to thedifferences α_(EX), β_(EX), Γ_(EX), Σ_(EX), Φ_(EX), respectively. In thepresent embodiment, the respective waveforms of the six exhaust-pressuresignals P_(EX) are obtained in the first covering manner, and therespective waveforms of the six intake-pressure signals P_(IN) areobtained in the second covering manner. Thus, more information about thecurrent state of the engine 90 is obtained than that obtained in thefourth embodiment.

[0321]FIG. 62 is a graph showing the respective changes of the positionPP of the first piston #1 and the intake pressure P_(IN) of the firstcylinder #1, with respect to the crank-shaft angle Θ_(crank), in thesecond covering manner. In the graph, as time, t, elapses, the angleΘ_(crank) decreases from 720 degrees toward 0 degree. The opening periodof the exhaust valves 48 or the intake valves 50 shown in FIG. 62 isobtained by reversing that shown in FIG. 6, with respect to a centerline corresponding to the angle Θ_(crank)=360 degrees. Accordingly, theopening and closing timings of the exhaust or intake valves 48, 50 shownin FIG. 62 are obtained by reversing those shown in FIG. 6, with respectto the center line. As is apparent from the comparison of FIGS. 6 and62, the change of the intake pressure P_(IN) shown in FIG. 62 is notcompletely identical with that obtained when the motor 125 is rotated inthe normal direction, but is very similar to the same. This fact can beutilized for determining a crank-shaft (CS) angle corresponding to theis timing when the intake valves 50 are closed. More specifically, theCS angle corresponding to the timing when the intake pressure P_(IN)starts decreasing from a constant value in the second covering manner isequal to the CS angle corresponding to the timing when the intake valves50 are closed. This angle (hereinafter, referred to as the“intake-pressure decrease-start angle”) is indicated by symbol,Θ_(INdec). The opening timing of the intake valves 50 and the openingand closing timings of the exhaust valves 48 are known in the firstcovering manner as shown in FIG. 6. Thus, in the present engine testingmethod, the control device 119 can accurately determine the respectiveCS angles corresponding to the opening and closing timings of theexhaust and intake valves 48, 50. However, it is noted that theintake-pressure maximal-value angle Θ_(INmax) shown in FIG. 6 differsfrom the intake-pressure maximal-value angle Θ_(INmax) shown in FIG. 62although each of the two angles corresponds to the timing when thecorresponding intake pressure P_(IN) takes a maximal value, because thetwo angles are obtained in the different covering manners.

[0322] When an engine test is actually carried out, the exhaust-pressuredecrease-start angle Θ_(EXdec), the exhaust-pressure maximal-value angleΘ_(EXmax), and the exhaust-pressure constant-value angle Θ_(EXconst)shown in FIG. 6 are obtained based on the exhaust pressure P_(EX)measured in the first covering manner. In the second covering manner,the intake-pressure decrease-start angle Θ_(INdec), the intake-pressuremaximal-value angle Θ_(INmax), and the intake-pressure constant-valueangle Θ_(INconst) shown in FIG. 62 are obtained based on the intakepressure P_(IN) measured. The angle Θ_(EXdec) corresponds to the timingwhen the exhaust valves 48 open when the engine 90 is rotated in thenormal direction. The angle Θ_(EXconst) and the angle Θ_(INmax)correspond to the timing when the exhaust valves 48 close when theengine 90 is rotated in the normal direction. However, in the case wherethe driven gear 40, 42 is one-tooth fast, the angle Θ_(EXconst) does notcorrespond to the closing timing of the exhaust valves 48, and theexhaust-pressure constant-start-angle difference SEX is produced (FIGS.22 and 50). Thus, the angle Θ_(INmax) should be employed. Meanwhile, theangle Θ_(INdec) corresponds to the timing when the intake valves 50close when the engine 90 is rotated in the normal direction, and theangle Θ_(EXmax) and the angle Θ_(INconst) correspond to the timing whenthe intake valves 50 open when the engine 90 is rotated in the normaldirection. However, in the case where the driven gear 40, 42 isone-tooth fast, the angle Θ_(INconst) does not correspond to the openingtiming of the intake valves 50, and the intake-pressureconstant-start-angle difference Σ_(IN) is produced. Thus, the angleΘ_(EXmax) should be employed. In the present embodiment, since theengine 90 can be rotated in both the first and second covering manners,the respective angles Θ_(crank) corresponding to the opening and closingtimings of the exhaust and intake valves 48, 50 are obtained.

[0323]FIG. 63 is a flow chart representing the main routine of an enginetesting program which is stored in the ROM of the fault finder 117 andwhich is carried out by the CPU and the RAM of the finder 117. First, atStep T1000, the CPU operates for establishing the first covering manneron the engine testing apparatus, and rotating the drive motor 125 in thenormal direction. Step T1000 is followed by Step T1002 to measure theexhaust pressure P_(EX) from each of the cylinders #1 to #6 of theengine 90 and obtain an exhaust-pressure maximal-value differenceα_(EX), an exhaust-pressure constant-value difference β_(EX), anexhaust-pressure maximal-value-angle difference Γ_(EX), anexhaust-pressure constant-start-angle difference Σ_(EX), and anexhaust-pressure decrease-start-angle difference Φ_(EX) of each cylinderfrom the corresponding exhaust pressure P_(EX) Subsequently, the controlof the CPU goes to Step T1004 to establish the second covering manner onthe testing apparatus, and rotate the drive motor 125 in the oppositedirection. Step T1004 is followed by Step T1006 to measure the intakepressure P_(IN) from each of the cylinders #1 to #6 of the engine 90 andobtain an intake-pressure maximal-value difference α_(IN), anintake-pressure constant-value difference β_(IN), an intake-pressuremaximal-value-angle difference Γ_(IN), an intake-pressureconstant-start-angle difference Σ_(IN), and an intake-pressuredecrease-start-angle difference Φ_(IN) of each cylinder from thecorresponding intake pressure P_(IN).

[0324] Subsequently, the control of the CPU goes to Step T1008 to call aforeign-matter-biting testing subroutine in which the CPU judges whetherthe foreign-matter biting has occurred to each cylinder. This test willbe described later. Step T1008 is followed by Step T1010 to carry outother tests than the foreign-matter-biting test. Those tests will alsobe described later. Subsequently, the control goes to Step T1012 tocommand, based on the contents of the fault flags, the display 118 tolight a lamp corresponding to the fault identified or specified at StepT1008 or Step T1010. Then, the CPU quits the main routine. The contentsof the flags ‘flag_(ina)’, ‘flag_(exa)’ are determined at Step T1008,and the contents of the other, eight flags are determined at Step T1010.

[0325]FIG. 64 is a flow chart representing the foreign-matter-bitingtest called at Step T1008 of FIG. 63. First, at Step T1100, the CPU sets0×01 to the variable ‘buf’ and, at Step T1102, the CPU initializes thevariable ‘i’ to 0 corresponding to the first piston or cylinder #1.Subsequently, at Step T1104, the CPU judges whether the value providedby a function, mod(β_(EXi)), corresponding to the current cylinder is 1.The function mod(x) is defined as a function which provides 1 if aparameter, x, changes by more than a reference amount, and provides 0 ifnot. Thus, a positive judgment is made at Step T1104 if theexhaust-pressure constant-value difference β_(EXi) changes by more thanthe reference amount. In the present embodiment, the reference amount isselected at 60, but any value may be employed as the reference amount solong as the value permits the CPU to judge whether the foreign-matterbiting has occurred to the exhaust valve or valves 48 of the cylinder,based on the difference β_(EXi). If a positive judgment is made at StepT1104, the control goes to Step T1106 to set the logical sum of thecontent of the fault flag ‘flag_(exa)’ and the content of the variable‘buf’, again to the flag ‘flag_(exa)’. Consequently one of the lower sixbits of the flag ‘flag_(exa)’ which corresponds to the current cylinderis changed to 1 indicating that the fault has occurred to that cylinder.Then, the control goes to Step T1108. On the other hand, if a negativejudgment is made at Step T1104, the control directly goes to Step T1108.

[0326] At Step T1108, the CPU judges whether the value provided by afunction, mod(β_(INi)), corresponding to the current cylinder is 1. Thatis, the CPU judges whether the intake-pressure constant-value differenceβ_(INi) changes by more than a reference amount. In the presentembodiment, this reference amount is also selected at 60. If a positivejudgment is made at Step T1108, the control goes to Step T1110 to setthe logical sum of the content of the fault flag ‘flag_(ina)’ and thecontent of the variable ‘buf’, again to the flag ‘flag_(ina)’.Consequently one of the lower six bits of the flag ‘flag_(ina)’ whichcorresponds to the current cylinder is changed to 1 indicating that thefault has occurred to that cylinder. Then, the control goes to StepT1112. On the other hand, if a negative judgment is made at Step T1108,the control directly goes to Step T1112. At Step T1112, the CPU adds oneto the content of the variable ‘i’. Step T1112 is followed by Step T1114to judge whether the content of the variable ‘i’ is equal to 6. If apositive judgment is made at Step T1114, the CPU quits the presentsubroutine. On the other hand, if a negative judgment is made, thecontrol goes to Step T1116 to shift 1 from the current bit to the next,higher bit in the variable ‘buf’, so that the number (0, 1, 2, 3, 4, or5) allotted to the bit having 1 coincides with the number indicated bythe content of the variable ‘i’. Then, the control of the CPU goes backto Step T1104. Thus, this foreign-matter-biting test provides a highlyreliable result obtained by judging whether the difference β_(EX) orβ_(IN) that does not change if the engine 90 does not have the fault offoreign-matter biting changes by more than the reference amount.

[0327] Next, there will be described the other tests carried out at StepT1010 of FIG. 63. At this step, a crank-pulley test, a cam-pulley test,a driven-gear test, a valve-clearance test, and a compression-ring testare carried out based on the differences α_(EX), β_(EX , Γ) _(EX),Σ_(EX), Φ_(EX), α_(IN), β_(IN), Γ_(IN), Σ_(IN), Φ_(IN) of each of thesix cylinders #1 to #6. Those tests are basically similar to thecrank-pulley test (FIG. 55), the cam-pulley test (FIG. 56), thedriven-gear test (FIG. 57), the valve-clearance test (FIG. 59), and thecompression-ring test (FIG. 60) employed in the fourth embodiment.However, since more information is utilized at Step T1010, a morereliable test result is obtained at this step.

[0328] For example, in the case where only whether the intake-valveclearance is small or not is judged (on the assumption for easierunderstanding that the other sorts of faults do not occur), thedifferences Φ_(IN), Σ_(IN) of each cylinder obtained in the secondcovering manner can be utilized. The differences Φ, Σ relating to theexhaust-valve clearance, indicated in the table of FIG. 50, can beregarded as those relating to the intake-valve clearance, obtained inthe second covering manner. That is, in the second covering manner,whether the intake-valve clearance is small or not influences thedifferences Φ_(IN), Σ_(IN). Therefore, if the intake-valve clearance issmall, and if it can be assumed that the influence of the smallintake-valve clearance to the differences Φ_(IN), Σ_(IN) is the same asthat to the differences Φ_(EX), Σ_(EX), the difference Φ_(IN) takes−6.4, and the difference Σ_(IN) takes 6.4. Thus, whether theintake-valve clearance is small can be judged by judging whether thedifference Φ_(IN) takes a negative value and simultaneously thedifference Σ_(IN) takes a positive value.

[0329] If the respective crank-shaft angles corresponding to the openingand closing timings of the intake valves 50 and the opening and closingtimings of the exhaust valves 48, measured from the engine 90 beingtested, are equal to those measured from a normal engine, the engine 90can be judged as a normal engine. Hence, the above-indicated anglesmeasured from the engine 90 are displayed on the display 118 togetherwith those measured from the normal engine. The display 118 may bereplaced by a display of a personal computer. In the latter case, thepersonal computer is connected to the control device 119 in such amanner that information can be interchanged between the two elements.The angles measured from the engine 90 are transferred from the controldevice 119 to the personal computer, so that the display of the computerdisplays the angles received from the control device 119. In addition,the display of the computer may display, for each cylinder, the graphsshown in FIGS. 6 and 62. In the last case, the differences between theangles measured from the engine 90 and those measured from the normalengine, if any, are indicated on those graphs. If the display of thecomputer indicates that a fault has occurred to the engine 90, then anoperator can perform a sensory test on the engine 90. This testingmethod is employed as a preliminary test or a screening test which helpsthe operator to identify or specify the fault which has occurred to theengine 90. Generally, the operator's identification or specification ofthe fault can be performed very quickly and very accurately. Inaddition, since the fault finder 117 of the control device 119 has onlyto judge whether an engine 90 being tested has a fault or not, thefinder 117 enjoys a simpler arrangement. In the present embodiment, thepressure sensor 98 is provided for each cylinder. If an orifice isformed through the covering member 458 of each cylinder, for restrictingair flowing therethrough, or if the degree of opening of the coveringmember 458 of each cylinder is adapted to be changeable, then the intakepressure P_(IN) of each cylinder can be obtained, in the first coveringmanner, independent of the respective intake pressures P_(IN) of theother cylinders. In this case, the engine 90 can be rotated in anincreased number of states, which contributes to improving thereliability of the present engine testing method, and/or increasing thenumber of sorts of faults are identified or specified by the same. Thisalso applies to the covering members 102, in the case where the engine90 is rotated in the second covering manner.

[0330] In the first covering manner, the engine 90 may be rotated in theopposite direction in addition to, or in place of in the normaldirection. Similarly, in the second covering manner, the engine 90 maybe rotated in the normal direction in addition to, or in place of in theopposite direction. In each case, the current state of the engine 90 isevaluated based on the obtained test result.

[0331] In each of the fourth and fifth embodiments, the V6 DOHC gasolineengines are tested. However, the present invention is applicable to thetesting of various types of engines. For example, in the case where SOHCengines are tested, the testing steps for finding the fault with thedriven gears 40, 42 are omitted. In addition, in the case where DOHCengines of the type wherein intake cam shafts (32, 34) are driven by notdriven gears (40, 42) but different cam pulleys, testing steps forfinding a fault with those different cam pulleys may be employed inplace of the testing steps for finding the fault with the driven gears.Meanwhile, in each of the fourth and fifth embodiments, the engine testis carried out based on the characteristic parameters of the exhaustpressures P_(EX) However, the other parameters indicated in the table ofFIG. 50 and/or the other characteristic parameters of the curves shownin the graphs of FIG. 8, etc. may be employed for the same purpose. Forexample, the maximum slope of the curve shown in FIG. 8, or thecrank-shaft angle corresponding to the maximum slope, the length and/orposition of the interval in which the rate of change of the curve isgreater than a reference value, etc. may be taken into account forfinding a fault or faults with an engine. The present invention may bealso applicable to diesel engines.

[0332] In order to specify or identify, with higher reliability, each ofa plurality of faults which simultaneously occur to a single engine, theengine testing apparatus can gather more information from the engine.For example, all possible combinations of presence or absence ofpredetermined faults are artificially created on an engine, and thetesting apparatus gathers a group of respective values of predeterminedparameters P_(EXmax), Θ_(EXmax), etc. in each of all the combinations ofthe predetermined faults created on the engine. Then, the testingapparatus obtains a group of respective values of the predeterminedparameters P_(EXmax), Θ_(EXmax), etc. from an engine being tested,compares the obtained group of values with each of the groups of valuesgathered in advance in all the fault combinations, and selects one ofall the fault combinations as the specified or identified faultcombination of the engine. In each of the fourth and fifth embodiments,the testing apparatus finds the one-tooth fast or slow state of thecrank pulley 20, the cam pulley 24, 26, or the driven gear 40, 42.However, the testing apparatus may be adapted to find the two or moreteeth fast or slow state of each pulley 20, 24, 26, 40, 42. In the lastcase, the parameters P_(EXmax), Θ_(EXmax), etc. may be classified inmore steps for finding a fault or faults with high accuracy. In thiscase, the slight differences of respective values of each of thoseparameters must be distinguished from each other. Since the enginetesting apparatus employed in each of the fourth and fifth embodimentscan quickly obtain a number of values of each of the parameters, it canfind a fault or faults with an engine with high reliability by, e.g.,statistically analyzing those values.

[0333] Next, there will be described a sixth embodiment of the presentinvention. The sixth embodiment is different from the above-describedfirst embodiment in that the engine testing routine of FIG. 25 employedin the first embodiment is replaced by a different engine testingroutine of FIG. 67 employed in the sixth embodiment. The engine testingapparatus of FIG. 4 employed in the first embodiment is also employed inthe sixth embodiment. Accordingly, the description of the testingapparatus is omitted. Thus, the present testing apparatus can providethe table shown in FIG. 24.

[0334] The respective values (in degrees) of the exhaust-pressuremaximal-value-angle difference Γ, the exhaust-pressureconstant-start-angle difference Σ, the exhaust-pressuredecrease-start-angle difference Φ, etc. indicated in the table of FIG.24 cannot be obtained unless, e.g., an actual value (in degrees) of theexhaust-pressure maximal-value angle Θ_(EXmax) of each cylinder isdetermined with respect to a reference value therefor (e.g., 0 degree)based on the output of the crank-shaft sensor 114. That is, the valuesof difference Γ indicated in the table of FIG. 24 cannot be obtained bycomparing the respective actual values of difference Γ of the cylinders#1 to #6 with one another, e.g., calculating the difference between therespective actual values of difference Γ of each pair of successivelyignited cylinders, or the difference between the respective actualvalues of difference Γ of each pair of successive odd-numbered (oreven-numbered) cylinders. This can be easily understood from therespective definitions of the differences Γ, Σ, Φ, etc. which have beendescribed in the first embodiment by reference to FIGS. 8, 11, etc.However, the values of differences Γ, Σ, Φ, etc. indicated in the tableof FIG. 24 are closely related to the information which is obtained bycomparing the respective actual values of each difference Γ, Σ, Φ, etc.of the cylinders #1 to #6 with one another. Therefore, there are somecases where even if the respective actual values of each difference Γ,Σ, Φ, etc. of the cylinders #1 to #6 with respect to a reference valuetherefor may not be known, at least one fault with the assembling of theengine 90 can be identified or specified based on the informationobtained by comparing the actual values of each difference Γ, Σ, Φ, etc.of the cylinders #1 to #6 with one another. Hereinafter, there will bedescribed those cases.

[0335] For example, an exhaust-pressure maximal-value-angle relativedifference, ΔΓ_(i) (i=1 to 6), is obtained by calculating the differencebetween the respective actual values of exhaust-pressure maximal-valueangle Θ_(EXmax) of each pair of successively ignited cylinders of thesix cylinders #1 to #6. The relative difference ΔΓ_(i) is obtained bysubtracting the angle Θ_(EXmax) of the cylinder #i from the angleΘ_(EXmax) of the cylinder #i+1. However, if the value, i +1, exceeds 6,it is reduced by 6. Similarly, an exhaust-pressure decrease-start-anglerelative difference, ΔΦ_(i), is obtained by calculating the differencebetween the respective actual values of exhaust-pressure decrease-startangle Θ_(EXdec) of each pair of successively ignited cylinders of thesix cylinders #1 to #6, and an exhaust-pressure constant-start-anglerelative difference, ΔΦ_(i), is obtained by calculating the differencebetween the respective actual values of exhaust-pressure constant-startangle Θ_(EXconst) of each pair of successively ignited cylinders. Therelative differences ΔΓ_(i), ΔΣ_(i), ΔΦ_(i) can be utilized for findingone or more faults with the assembling of the engine 90, as describedbelow.

[0336]FIG. 65 is a graph showing the respective values of relativedifferences ΔΓ_(i), ΔΣ_(i), ΔΦ_(i) obtained from the waveform of exhaustpressure P_(EX) of each of the six cylinders #1 to #6. The respectivevalues of relative differences ΔΓ_(i), ΔΣ_(i), ΔΦ_(i) can be obtainedwithout needing the output of the CS sensor 114. For example, the sixvalues of relative difference ΔΓ_(i) are obtained by measuring, using atimer (not shown) provided in the fault finder 117, a time when theoutput of each of the six pressure sensors 106 takes a maximal value,and calculating the difference between the respective measured times ofeach pair of successively ignited cylinders of the six cylinders #1 toto #6 with one another. Hereinafter, there will be described thosecases.

[0337] For example, an exhaust-pressure maximal-value-angle relativedifference, ΔΓ_(i) (i=1 to 6), is obtained by calculating the differencebetween the respective actual values of exhaust-pressure maximal-valueangle Θ_(EXmax) of each pair of successively ignited cylinders of thesix cylinders #1 to #6. The relative difference ΔΓ_(i) is obtained bysubtracting the angle Θ_(EXmax) of the cylinder #i from the angleΘ_(EXmax) of the cylinder #i+1. However, if the value, i+1, exceeds 6,it is reduced by 6. Similarly, an exhaust-pressure decrease-start-anglerelative difference, ΔΣ_(i), is obtained by calculating the differencebetween the respective actual values of exhaust-pressure decrease-startangle Θ_(EXdec) of each pair of successively ignited cylinders of thesix cylinders #1 to #6, and an exhaust-pressure constant-start-anglerelative difference, ΔΦ_(i), is obtained by calculating the differencebetween the respective actual values of exhaust-pressure constant-startangle Θ_(EXconst) of each pair of successively ignited cylinders. Therelative differences ΔΓ_(i), ΔΣ_(i)ΔΦ_(i) can be utilized for findingone or more faults with the assembling of the engine 90, as describedbelow.

[0338]FIG. 65 is a graph showing the respective values of relativedifferences ΔΓ_(i), ΔΣ_(i), ΔΦ_(i) obtained from the waveform of exhaustpressure P_(EX) of each of the six cylinders #1 to #6. The respectivevalues of relative differences ΔΓ_(i), ΔΣ_(i), ΔΦ_(i) can be obtainedwithout needing the output of the CS sensor 114. For example, the sixvalues of relative difference ΔΓ_(i) are obtained by measuring, using atimer (not shown) provided in the fault finder 117, a time when theoutput of each of the six pressure sensors 106 takes a maximal value,and calculating the difference between the respective measured times ofeach pair of successively ignited cylinders of the six cylinders #1 to#6. Thus, six time differences are obtained. Each of the six timedifferences is converted into an crank-shaft (CS) angle (in degrees) bydividing each time difference by the sum of the six time differences andmultiplying the thus obtained value by 720 degrees corresponding to onecycle. In addition, the relative difference ΔΓ_(i) can be obtained byidentifying a time when the exhaust pressure P_(EX) of each cylinder #1to #6 represented by the output of the corresponding pressure sensor 106changes from a constant state in which the pressure P_(EX) takes asubstantially constant value, to a first decreasing state in which thepressure P_(EX) quickly decreases. As is apparent from FIG. 6, regardingthe engine 90 being tested, the constant state of the exhaust pressureP_(EX) of each cylinder #1 to #6 occupies more than 60% of the totaltime of each cycle. The six values of relative difference ΔΦ_(i) areobtained by calculating the difference between the respective identifiedtimes of each pair of successively ignited cylinders of the sixcylinders #1 to #6, like the six values of relative difference ΔΓ_(i).The relative difference ΔΣ_(i) can be obtained, contrary to the mannerin which the relative difference ΔΦ_(i) is obtained, by identifying atime when the exhaust pressure P_(EX) of each cylinder #1 to #6 changesfrom a second decreasing state different from the first decreasingstate, to the constant state. Hereinafter, the above-indicated mannerswill be referred to as the “time-difference-dependentrelative-angle-difference obtaining manners”.

[0339] The respective values of relative differences ΔΓ_(i), ΔΣ_(i),ΔΦ_(i) are influenced by the two values of exhaust-pressuremaximal-value-angle difference Γ_(i), Γ_(i+1), the two values ofexhaust-pressure decrease-start-angle difference Φ_(i), Φ_(i+1), and thetwo values of exhaust-pressure constant-start-angle difference Σ_(i),Σ_(i+1), respectively. That is, the respective values of relativedifferences ΔΓ_(i), ΔΣ_(i), ΔΦ_(i) are influenced by the assembled stateof the engine 90. For example, in the case where the right cam pulley 26of the right bank of the engine 90 is one-tooth fast as indicated inFIG. 65, the six values of relative difference ΔΓ_(i) (i.e., ΔΓ₁, ΔΓ₂,ΔΓ₃, ΔΓ₄, ΔΓ₅, ΔΓ₆ corresponding to the six cylinders #1 to #6,respectively, indicated in FIG. 66, are measured from the engine 90. Thesix numerals, 1, 2, 3, 4, 5, 6, provided along the outermost circleshown in FIG. 66 represent the six cylinders #1 to #6, respectively, andthe respective angular positions of the six numerals representrespective angular phases at which the respective exhaust pressuresP_(EX) of the six cylinders take respective maximal values in the casewhere the engine 90 is normal. The full circle corresponds to 720degrees of the CS angle. Since in the present embodiment it is notneeded to specify the angular position corresponding to the zero degreeof the CS angle, that position is not shown in the figure. If the engine90 is normal, each of the six values of relative difference ΔΓ_(i)(i.e., ΔΓ₁ to ΔΓ₆) is 120 degrees (=720 (degrees)/6 (cylinders)). Thisangle will be referred to as the “exhaust-pressure maximal-value-angleaverage relative difference, ΔΓ_(m)”.

[0340] In the case where the right cam pulley 26 of the engine 90 isone-tooth fast, the respective values (Γ₁, Γ₃, Γ₅) of difference Γ ofthe odd-numbered cylinders #1, #3, #5 of the left bank are zero butthose (Γ₂, Γ₄, Γ₆) of the even-numbered cylinders #2, #4, #6 of theright bank are not zero. Regarding the example shown in FIG. 24,Γ₁=Γ₃=Γ₅=0 and Γ₂=Γ₄=Γ₆=−15. The relative difference ΔΓ_(i) is definedby the following expression:

ΔΓ_(i)=ΔΓ_(m)+Γ_(i+1)−Γ_(i)  (12)

[0341] The six values ΔΓ₁ to ΔΓ₆ of relative difference ΔΓ_(i) areobtained by using the expression (12), as follows:

[0342] ΔΓ₁=ΔΓ_(m)+Γ₂−Γ₁=120+(−15)−0=105

[0343] ΔΓ₂=ΔΓ_(m)+Γ₃−Γ₂=120+0−(−15)=135

[0344] ΔΓ₃=ΔΓ_(m)+Γ₄−Γ₃=120+(−15)−0=105

[0345] ΔΓ₄=ΔΓ_(m)+Γ₅−Γ₄=120+0−(−15)=135

[0346] ΔΓ₅=ΔΓ_(m)+Γ₆−Γ₅=120+(−15)−0=105

[0347] ΔΓ₆=ΔΓ_(m)+Γ₁−Γ₆=120+0−(−15)=135

[0348] In the case where the variable i=6, the value, i+1, is reduced by6 to 1, as defined above. Thus, the phases indicated at the numerals 2,4, 6 which are obtained when the engine 90 is normal move to the phasesindicated at the numerals 2′, 4′, 6′ which are obtained when the engine90 has the one-tooth fast state of the right cam pulley 26.

[0349] The relative differences ΔΦ_(i), ΔΣ_(i) are defined by thefollowing expressions, respectively:

ΔΦ_(i)=ΔΦ_(m)+Φ_(i+1)−Φ_(i)  (13)

ΔΣ_(i)=ΔΣ_(m)+Σ_(i+1)−Σ₈  (14)

[0350] The average relative differences ΔΓ_(m), ΔΦ_(m), ΔΣ_(m) are equalto 120 degrees. In the case where the actual values indicated in thetable of FIG. 24 have already been known, the respective values of threerelative differences ΔΓ_(i), ΔΦ_(i), ΔΣ_(i) corresponding to each of theassembling faults are obtained by replacing the difference ofappropriate terms, Γ_(i+1)−Γ_(i), Φ_(i+1)−Φ_(i), or Σ_(i+1)−Σ_(i), ineach of the expressions (12) to (14) with the difference of appropriatevalues, indicated in the table, which correspond to the each fault. Inthe case where a plurality of faults simultaneously occur to the singleengine 90, the respective values of three relative differences ΔΓ_(i),ΔΦ_(i), ΔΣ_(i) corresponding to the simultaneous occurrence of theplurality of faults are obtained by replacing the difference ofappropriate terms in each of the expressions (12) to (14) with the sumof respective differences of appropriate values which correspond to theplurality of faults. However, converses are not always true. In the casewhere there is some possibility that a plurality of unspecified faultssimultaneously occur to the engine 90, those faults may not be specifiedbased on only the respective values of relative differences ΔΓ_(i),ΔΦ_(i), ΔΣ_(i) which are obtained in the above-describedtime-difference-dependent relative-angle-difference obtaining manners.

[0351] For example, as is apparent from FIG. 24, in the case where thecrank pulley 18 is one-tooth fast or slow, or in the case where both theleft and right cam pulleys 24, 26 or both the left and right drivengears 40, 42 are one-tooth fast or slow, all the cylinders #1 to #6 havethe same values of differences Γ, Φ, Σ. Accordingly, the threeexpressions (12), (13), (14) showΔΓ_(i)=ΔΓ_(m)=ΔΦ_(i)=ΔΦ_(m)=ΔΣ_(i)=ΔΣ_(m)=120 (degrees). This result isthe same as that obtained when the engine 90 is normal. In addition, thecase where the right cam pulley 26 is one-tooth fast and the left campulley 24 is normal, cannot be distinguished from the case where theright cam pulley 26 is normal and the left cam pulley 24 is one-toothslow. Moreover, the case where the intake vales 50 or the exhaust valves48 of all the cylinders #1 to #6 have the same clearance fault (e.g.,small clearance) cannot be identified from the case where the engine 90is normal. Thus, the present engine testing method that relies on therelative differences ΔΓ_(i), ΔΦ_(i), ΔΣ_(i) is not always effective injudging whether the engine 90 being tested is normal or not. However, asdescribed below, the present testing method can specify at least one“candidate” for a plurality of faults, in the case where there is somepossibility that the plurality of faults have simultaneously occurred tothe single engine 90. However, the candidate or candidates specified bythe present method may not include the fault, or all the faults, whichhas or have actually occurred to the engine 90. If at least onecandidate is specified, then an operator can actually check thecandidate on the engine 90. If the candidate is found as a fault, theoperator corrects the fault, and the present testing method may beperformed once again on the engine 90. Thus, the present testing methodcan effectively prevent itself from judging that the engine 90 isnormal, notwithstanding the presence of one or more faults with theengine 90.

[0352]FIG. 67 is a flow chart representing the main routine of anassembled engine testing program which is stored in the ROM of the faultfinder 117 and which is carried out by the CPU and the RAM of the finder117. According to the main routine, the fault finder 117 identifies thepresence or absence of one or more assembling faults of the engine 90,based on the respective exhaust-pressure maximal values corresponding tothe six pistons or cylinders #1 to #6. If the engine 90 has no fault,the finder 117 commands the display 118 (FIG. 26) to indicate that theengine 90 has passed the test. On the other hand, if a fault is found,the finder 117 identifies or specifies what is the fault and commandsthe display 118 to indicate that the engine 90 has not passed the test,and the place where the fault has occurred.

[0353] First, at Step U102, the fault finder 117 or the CPU thereofinitializes a variable ‘count’ to count=0. At Step U104, the CPUinitializes a variable ‘i’ to i=0 corresponding to the first piston orcylinder #1. The number greater by one than the variable ‘i’ is equal tothe number of the current piston or cylinder. Subsequently, at StepU106, the CPU judges whether both the respective absolute values ofexhaust-pressure maximal-value difference .i and exhaust-pressureconstant-value difference β_(i) which are measured from the currentcylinder #i+1 are smaller than 3. If a negative judgment is made at StepU106, the control of the CPU goes to Step U108 to add one to thevariable ‘count’. On the other hand, if a positive judgment is made atStep U106, the control goes to Step U110 to judge whether the variable‘i’ is equal to 5 corresponding to the sixth piston #6. If a negativejudgment is made at Step U110, the control goes to Step U111 to add oneto the variable ‘i’ and then goes back to Step U106.

[0354] As can be understood from FIG. 24, it can be concluded that ifthe respective absolute values of differences α, β are smaller than 3,the test engine 90 has normally been assembled without any fault.

[0355] If a positive judgment is made at Step U110, the control of theCPU goes to Step U112 to judge whether the variable ‘count’ is equal to0. If a positive judgment is made at Step U112, the control goes to StepU114 to command the display 118 to light the OK lamp 200 of the display118 indicating that no fault has been found. Thus, the CPU quits themain routine. On the other hand, if a negative judgment is made at StepU112, that is, a fault has been found, the control goes to Step U116 tolight the NG lamp 202 of the display 118 indicating the above situation.Subsequently, the control goes to Step U118, i.e., a fault identifyingor specifying subroutine. Step U118 is followed by Step U120 to light alamp or lamps of the display 118 which corresponds or correspond to thefault or faults specified at Step U118. Then, the CPU quits the mainroutine.

[0356] The OK lamp 200 is lit when no fault is found. The NG lamp 202 islit when one or more faults are found. In the case where one or morefaults is or are found and specified, the control device 119 may lightone or more of the fault lamps 204, 206, 208, 210, 212, 214, 216, 218,220, 222 which corresponds or correspond to the specified fault orfaults. In addition, the CPU may light, for each of the pistons #1 to#6, one or more of the fault lamps 224, 226, 228, 230, 232 whichcorresponds to the specified fault or faults. Moreover, in the casewhere one or more faults cannot be specified as will be described later,that is, in the case where there is some possibility that the engine 90has one or more faults but it cannot be concluded that the engine 90does have one or more faults, one or more fault lamps corresponding tothe doubtful fault or faults is or are flashed.

[0357]FIG. 68 is a flow chart representing the fault specifyingsubroutine of Step U118 of FIG. 67. First, at Step U200, the CPU of thefault finder 117 initializes, to 0×00, each of eight fault flagscorresponding to the faults indicated in the table of FIG. 24. As shownin FIG. 69, each of the eight flags comprises one byte data, i.e., eightbits data. If no fault has been found, each flag remains 0×00. The lowerfour bits of the flag ‘flag_(drvn)’ correspond to the fast and slowstates of the left and right driven gears 40, 42, and the lower fourbits of the flag ‘flag_(cam)’ correspond to the fast and slow states ofthe left and right cam pulleys 24, 26. The lower two bits of the flag‘flag_(crnk)’ correspond to the fast and slow states of the crank pulley20. The lower six bits of the flags ‘flag_(ins)’, ‘flag_(inl)’,‘flag_(exs)′, ‘flag_(exl)′, ‘flag_(ring)’ correspond to the presence orabsence of the small and large intake-valve clearances, the small andlarge exhaust-valve clearances, and the compression-ring missing,respectively, of the six pistons or cylinders #1 to #6. The respectivehighest and second highest bits (i.e., “7” and “6” bits shown in FIG.69) of each of the eight flags are doubtful-fault bits (hereinafter,referred to as the “error-1” bit and the “error-2” bit, respectively).When the value of 0 is set in the error-1 bit of each one of thoseflags, the value of 0 is also set in the error-2 bit of the same flag.In this case, the remaining bits of the flag are used to indicate thetest result. However, when the value of 1 is set in the error-1 bit, thevalue of 0 or 1 is set in the error-2 bit. In this case, the value of 0set in the error bit 2 of each flag indicates that the engine 90 mayhave one or more faults corresponding to another or other bits of theflag (except for the nonsense bits indicated at “-” in FIG. 69) whichhas or have the value of 0. In this case, the fault lamp or lampscorresponding to one or more of the lower six bits which has or have thevalue of 0 is or are flashed (i.e., alternately turned on and off).Meanwhile, the value of 1 set in the error bit 2 of each flag indicatesthat the engine 90 may have one or more faults corresponding to anotheror other bits of the flag which has or have the value of 1. In thesecond case, the fault lamp or lamps corresponding to one or more of thelower six bits which has or have the value of 1 is or are flashed. Inother words, in the first case, it is concluded that the engine 90 hasone or more faults corresponding to the bit or bits having the value of1 and, in the second case, it is concluded that the engine 90 does nothave any faults corresponding to the bit or bits having the value of 0.In addition, in the first case, the lamp or lamps corresponding to thebit or bits having the value of 0 is or are flashed and the lamp orlamps corresponding to the bit or bits having the value of 1 is or arelit and, in the second case, the lamp or lamps corresponding to the bitor bits having the value of 1 is or are flashed and the lamp or lampscorresponding to the bit or bits having the value of 0 is or are notlit.

[0358] Step U200 is followed by Steps U202 to U214. Step U202 is aone-tooth-fast-driven-gear test for determining values to be set to thefault flag ‘flag_(drvn)’, Step U204 is a small-exhaust-valve-clearancetest for determining values to be set to the flag ‘flag_(exs)’. StepU206 is a cam-pulley test for determining values to be set to the flag‘flag_(cam)’. Step U208 is a one-tooth-slow-driven-gear andintake-valve-clearance test for determining values to be set to theflags flag_(drvn)’, ‘flag_(ins)’, ‘flag_(inl)’ Step U210 is alarge-exhaust-valve-clearance test for determining values to be set tothe flag ‘flag_(exl)’. Step U212 is a compression-ring-missing test fordetermining values to be set to the flag ‘flag_(ring)’. Step U212 isfollowed by Step U214, i.e., a complementary step which will bedescribed later. The present fault specifying subroutine does notinclude any test for specifying the fast or slow state of the crankpulley 18. Accordingly, if a negative judgment is made at Step U112, thevalue of 1 is set in the error-1 (highest) bit of the fault flag‘flag_(crnk)’.

[0359]FIG. 70 is a flow chart representing theone-tooth-fast-driven-gear test called at Step U202 of FIG. 68. In thistest, the CPU of the fault finder 117 judges whether the driven gear 40,42 of the left or right bank is one-tooth fast, based on theexhaust-pressure decrease-start-angle relative difference Φ_(i) and theexhaust-pressure constant-start-angle relative difference ΔΣ_(i) of thecylinder indicated by a variable ‘i’ (i=1 to 6), irrespective of whetherthe engine 90 has another or other faults. As indicated above, the casewhere both of the left and right driven gears 40, 42 are one-tooth fastand the case where both the two driven gears 40, 42 are normal cannot beidentified or distinguished from each other. This fact is indicated byflashing both the fast-left-driven-gear lamp 216 and thefast-right-driven-gear lamp 220.

[0360] First, at Step U300, the CPU calculates a variable, ζ_(i), foreach cylinder #1 to #6 based on the relative differences ΔΦ_(i), ΔΣ_(i)of the same, according to the following expression:

ζ_(i)=(ΔΣΦ_(i)+ΔΦ_(i))%30  (15)

[0361] The relative differences ΔΦ_(i), ΔΣ_(i) of each cylinder areobtained by analyzing the waveform of the exhaust-pressure signal P_(EX)detected from the cylinder, as described above. The symbol “%” is aso-called modular operator, and “a%b” indicates the remainder obtainedby dividing the value of “a” by the value of “b”. Hereinafter, thevariable ζ_(i) will be indicated by ζ_(odd) when the variable ‘i’ is anodd number, i.e., when the current cylinder is a cylinder of the leftbank, and by even when the variable ‘i’ is an even number, i.e., whenthe current cylinder is a cylinder of the right bank.

[0362] The reason why the relative differences ΔΦ_(i), ΔΣ_(i) are addedto each other in the expression (15) defining the variable ζ_(i) is toeliminate the respective influences of the fault of small exhaust-valveclearance that may have occurred to the current cylinder with respect tothe relative differences ΔΦ_(i), ΔΣ_(i). More specifically described,the respective influences of the small exhaust-valve clearance to therelative differences ΔΦ_(i), ΔΣ_(i) have different signs andsubstantially equal absolute values. However, the absolute values of theinfluences of the large or small exhaust-valve clearance to the relativedifferences ΔΦ_(i), ΔΣ_(i) are changeable. In fact, in the case wherethe current cylinder has the fault of small exhaust-valve clearance, theexhaust-pressure constant-start-angle difference Σ is changeable in therange of from 2 to 10. The actual value, 6.4, of the difference Σindicated in the table of FIG. 24 is just an example falling in thisrange. However, when the absolute value of the influence to thedifference Σ and accordingly to the relative difference ΔΣ_(i) change,also do the absolute value of the influence to the difference Φ andaccordingly to the relative difference ΔΦ_(i). Since those influenceshave opposite signs, the sum of them is not influenced by the smallexhaust-valve clearance. The sum of relative differences ΔΦ_(i), ΔΣ_(i),i.e., ΔΦ_(odd)+ΔΣ_(odd), or ΔΦ_(even)+ΔΣ_(even), must be calculatedbased on the respective values of relative differences ΔΦ_(i), ΔΣ_(i)obtained from a single odd-numbered or even-numbered cylinder.

[0363] Meanwhile, the fault of large exhaust-valve clearance does notinfluence the exhaust-pressure constant-start-angle difference Σ nor theexhaust-pressure decrease-start-angle difference Φ. Therefore, the sumof relative differences ΔΦ_(i), ΔΣ_(i) is not influenced by the small orlarge exhaust-valve clearance.

[0364] The reason why the variable ζ_(i) is defined by the remainderobtained when the sum of relative differences ΔΦ_(i), ΔΣ_(i) is dividedby 30 is that the sum is influenced by the one-tooth fast or slow stateof the left or right cam pulley 24, 26 that may have occurred to thebank corresponding to the current cylinder, in such a manner that thesum is stepwise increased or decreased in units of 30 (i.e., 15+15=30).Meanwhile, the influences of the one-tooth fast state of the driven gear40, 42 are smaller than 30. Thus, the variable defined by the expression(15) is free from the influences of the fast or slow state of the campulley 24, 26 as well as the small or large exhaust-valve clearance.Accordingly, the variable ζ_(i) is influenced M by the one-tooth faststate of either the left or right driven gear 40, 42.

[0365] The following expression (16) is obtained by replacing, in theexpression (15), the relative differences ΔΦ_(i), ΔΣ_(i) with thosedefined by the expressions (13) and (14):

ζ_(i)=(ζΣ_(m)+Σ_(i+1)−Σ_(i)+ζΦ_(m)+Φ_(i+1)−Φ_(i))%30   (16)

[0366] In the above expression, the exhaust-pressureconstant-start-angle average relative difference ΔΣ_(m) and theexhaust-pressure decrease-start-angle average relative difference ΔΦ_(m)are both equal to 120 degrees. Thus, the variable ζ_(i) can becalculated from the respective values of differences Σ, Φ indicated inthe table of FIG. 24. In actual engine tests, those values ofdifferences ΣΦ are unknown, and the variable ζ_(i) is calculatedaccording to the expression (15). However, since the expression (16) ismore convenient than the expression (15), the following description willbe made by reference to the expression (16).

[0367] Step U300 is followed by Step U302 to identify which one of threecombinations, (0, 0), (8.4, 21.6) and (21.6, 8.4), is taken by thecombination, (ζ_(odd), ζ_(even)), of respective values of variable ζ_(i)for an odd-numbered cylinder and an even-numbered cylinder. Thecombination (ζ_(odd), ζ_(even)) can only take one of the above threecombinations, for the following reasons:

[0368] In the case where the engine 90 does not have any faultsincluding the faults with the driven gears 40, 42, the relativedifferences ΔΣ_(odd), ΔΣ_(even) and the relative differences ΔΦ_(odd),ΔΦ_(even) take the following values:

[0369] ΔΣ_(odd)=ΔΣ_(m)+Σ_(even)−Σ_(odd)=120+0−0=120

[0370] ΔΣ_(even=ΔΣ) _(m)+Σ_(odd)−Σ_(even)=120+0−0=120

[0371] ΔΦ_(odd)=ΔΦ_(m)+Φ_(even)−Φ_(odd)=120+0−0=120

[0372] ΔΦ_(even=ΔΦm)+Φ_(odd)−Φ_(even)=120+0−0=120

[0373] The variables ζ_(odd), ζ_(even) are calculated from the abovevalues, as follows:

[0374] ζ_(odd)=(ΔΦ_(odd))%30=(120+120)%30=0

[0375] ζ_(even)=(ΔΣ_(even)+ΔΦ_(even))%30=(120+120)%30=0

[0376] In the case where the left driven gear 40 is one-tooth fast andthe engine 90 does not have any other faults, the relative differencesΔΣ_(odd), ΔΣ_(even), ΔΦ_(odd), ΔΦ_(even) take the following values:

[0377] ←Σ_(odd)=ΔΣ_(m)+Σ_(even)−Σ_(odd)=120+0−(−8.4)=128.4

[0378] ΔΣ_(even=ΔΣm)+Σ_(odd)−Σ_(even)=120+(−8.40−0=111.6

[0379] ΔΦ_(odd)=ΔΦ_(m)+Φ_(even)−Φ_(odd)=120+0−0=120

[0380] ΔΦ_(even=ΔΦm)+Φ_(odd)−Φ_(even)=120+0−0=120

[0381] The variables ζ_(odd), ζ_(even) are calculated from the abovevalues, as follows:

[0382] ζ_(odd)=(ΔΣ_(odd)+ΔΦ_(odd))%30=(128.4+120)%30=8.4

[0383] ζ_(even)=(ΔΣ_(even)+ΔΦ_(even))%30=(111.6+120)%30=21.6

[0384] In the case where the right driven gear 42 is one-tooth fast andthe engine 90 does not have any other faults, the relative differencesΔΣ_(odd), ΔΣ_(even), ΔΦ_(odd), ΔΦ_(even) take the following values:

[0385] ΔΣ_(odd)=ΔΣ_(m)+Σ_(even)−Σ_(odd)=120+(−8.4)−0=111.6

[0386] ΔΣ_(even=ΔΣm)+Σ_(odd)−Σ_(even)=120+0−(−8.4)=128.4

[0387] ΔΦ_(odd)=ΔΦ_(m)+Φ_(even)−Φ_(odd)=120+0−0=120

[0388] ΔΦ_(even=ΔΦm)+Φ_(odd)−Φ_(even)=120+0−0=120

[0389] The variables ζ_(odd), ζ_(even) are calculated from the abovevalues, as follows:

[0390] ζ_(odd)=(ΔΣ_(odd)+ΔΦ_(odd))%30=(111.6+120)%30=21.6

[0391] ζ_(even)=(ΔΦ_(even)+ΔΦ_(even) 0%30=(128.4+120)%30=8.4

[0392] For the above reasons, when the engine 90 has no fault, thecombination (ζ_(odd), ζ_(even)) takes (0, 0); when the left driven gear40 is one-tooth fast, the combination takes (8.4, 21.6); and when theright driven gear 42 is one-tooth fast, the combination takes (21.6,8.4).

[0393] In the case where the CPU identifies at Step U302 that thecombination (ζ_(odd), ζ_(even)) is equal to (0, 0), the control of theCPU goes to Step U304 to set, in the fault flag ‘flag_(drvn)’ thelogical sum, 0×C5, of (a) 0×05 that is the logical sum of 0×01indicating that the left driven gear 40 is one-tooth fast and 0×04indicating that the right driven gear 42 is one-tooth fast and (b) 0×C0indicating that the value of 1 is set in each of the error-1 and error-2(highest and second highest) bits of the flag ‘flag_(drvn)’. Based onthe content of the flag ‘flag_(drvn)’, the CPU commands the display 118to flash both the lamps 216, 220 as described above. In the case wherethe CPU identifies at Step U302 that the combination (ζ_(odd), ζ_(even))is equal to (8.4, 21.6), the control of the CPU goes to Step U306 toset, in the flag ‘flag_(drvn)’, 0×01 indicating that the left drivengear 40 is one-tooth fast. In the case where the CPU identifies at StepU302 that the combination (ζ_(odd), ζ_(even)) are equal to (21.6, 8.4),the control of the CPU goes to Step U308 to set, in the flag‘flag_(drvn)’, 0×04 indicating that the right driven gear 42 isone-tooth fast.

[0394] However, strictly, the above conclusion that the combination(odd’ seven) can only take one of the three combinations (0, 0), (8.4,21.6), (21.6, 8.4) is not correct. In fact, the variables ζ_(odd),ζ_(even) may contain errors. Those errors can be measured, and themeasured errors fall in, e.g., the range of from −2 to 2. Therefore, thecombination (ζ_(odd), ζ_(even)) falls in one of three range combinations(from −2 to 2, from −2 to 2), (from 6.4 to 10.4, from 19.6 to 23.6), and(from 19.6 to 23.6, from 6.4 to 10.4). The CPU can easily identify inwhich range the combination (ζ_(odd), ζ_(even)) falls.

[0395] The combination (ζ_(odd), ζ_(even)) obtained from one pair ofodd-numbered and even-numbered cylinders may be used alone. However, theformer combination (ζ_(odd)’, ζ_(even)) may be used with another orother combinations obtained from another or other pairs of odd-numberedand even-numbered cylinders. For example, the average of respectivevalues of variable ζ_(odd) for the three odd-numbered cylinders #1, #3,#5 may be combined with the average of respective values of variableζ_(even) for the three even-numbered cylinders #2, #4, #6.

[0396] Thus, it can be said that the one-tooth-fast driven-gear testindicated in FIG. 70 is carried by comparing the variable ζ_(i) of atleast one odd-numbered cylinder with that of at least one even-numberedcylinder.

[0397] Otherwise, it can be said that the test is carried out bygrouping the respective values of variable ζ_(i) for all the sixcylinders, into a first group including the values for the odd-numberedcylinders and a second group including the values for the even-numberedcylinders, and then comparing one or more values of one of the twogroups with one or more values of the other group.

[0398]FIG. 71 shows a flow chart representing thesmall-exhaust-valve-clearance test called at Step U204 of FIG. 68.

[0399] First, at Step U400, the CPU calculates a variable, η_(i), foreach cylinder #1 to #6, based on the relative differences ΔΦ_(i), ΔΣ_(i)of the same, according to the following expression (17):

η_(i)={ΔΦ_(i)−ΔΣ_(i) −f(ζ_(i))}/2  (17)

[0400] The relative differences ΔΦ_(i), ΔΣ_(i) of each cylinder areobtained by analyzing the waveform of the exhaust-pressure signal P_(EX)detected from the cylinder, as described above. The function, f(ζ_(i)),is employed for eliminating the influence of the one-tooth fast state ofthe left or right driven gear 40, 42 that may be contained in therelative difference ΔΣ_(i). The variable ζ_(i) is obtained according tothe expression (15). The function f(ζ_(i)) provides −8.4 when the drivengear 40, 42 corresponding to the bank including the current cylinder isone-tooth fast; 8.4 when the driven gear 40, 42 corresponding to theother bank than the bank including the current cylinder is one-toothfast; and 0 when both of the two driven gears 40, 42 are normal (or bothare one-tooth fast). Thus, the function f(ζ_(i)) provides the samevalue, 0, both when the two driven gears 40, 42 are normal and when thetwo gears 40, 42 are one-tooth fast. However, this does not influencethe result of the present test about whether the current cylinder hasthe fault of small exhaust-valve clearance.

[0401] The following expression (18) is obtained by replacing, in theexpression (17), the relative differences ΔΦ_(i), ΔΣ_(i) with thosedefined by the expressions (13) and (14):

η_(i)={(ΔΦ_(m)+Φ_(i+1)−Φ_(i))−(ΔΣ_(m)+Σ_(i+1)−Σ_(i))−f(ζ_(i))}/2

={Φ_(i+1)−Φ_(i)−(Σ_(i+1)−Σ_(i))−f(ζ_(i))}/2   (18)

[0402] The above expression (18) is obtained by using the fact that boththe average relative difference ΔΣ_(m) and the average relativedifference ΔΦ_(m) are equal to 120 degrees. Thus, the variable η_(i) canbe calculated from the respective values of differences Σ, Φ indicatedin the table of FIG. 24 and the value provided by the function f(ζ_(i)).The thus calculated values of variable η_(i) are equal to those whichare calculated according to the expression (17) in actual engine tests.

[0403] For example, in the case where the first cylinder #1 has thefault of small exhaust-valve clearance and each of the two driven gears40, 42 is not one-tooth fast, the value of variable η_(i) for eachcylinder is obtained as follows:

[0404] η₁={Φ₂−Φ₁−(Σ₂−Σ₁)−f(ζ₁)}/2={0−(−6.4)−(0−6.4)−0}/2=6.4

[0405] η₂={Φ₃−Φ₂−(Σ₃−Σ₂)−f(ζ₂)}/2={0−0−(0−0)−0}/2=0

[0406] η₃={Φ₄−Φ₂−(Σ₄−Σ₃)−f(ζ₃)}/2={0−0−(0−0)−0}/2=0

[0407] η₄={Φ₆−Φ₅−(Σ₆−Σ₅)−f(ζ₅)}/2={0−0−(0−0)−0}/2=0

[0408] η₆={Φ₁−Φ₆−(Σ₁−Σ₆ 0−f(ζ₆)}/2={0−0−(0−0)−0}/2=0

[0409] In addition, in the case where the first and second cylinders #1,#2 have the fault of small exhaust-valve clearance and each of the twodriven gears 40, 42 is not one-tooth fast, the value of variable η_(i)for each is cylinder is obtained as follows:

[0410] η₁={Φ₂−Φ₁−(Σ₂−Σ₁)−f(ζ₁)}/2={0−(−6.4)−(−6.4)−(6.4−6.4)−0}/2=0

[0411] η₂={Φ₃−Φ₂−(Σ₃−Σ₂)−f(ζ₂)}/2={0−(−6.4)−0−6.4)−0}/2=6.4

[0412] η₃={Φ₄−Φ₂−(Σ₄−Σ₃)−f(ζ₃)}/2={0−0−(0−0)−0}/2=0

[0413] η₄={Φ₅−Φ₄−(Σ₅−Σ₄)−f(ζ₅)}/2={0−0−(0−0)−0}/2=0

[0414] η₆={Φ₁−Φ₆−(Σ₁−Σ₆)−f(ζ₆)}/2={−6.4−0−(6.4−0)−0}/2=−6.4

[0415] Moreover, in the case where the first, second and fifth cylinders#1, #2, #5 have the fault of small exhaust-valve clearance and only theright driven gear 42 is one-tooth fast, the value of variable η_(i) foreach cylinder is equal to the value obtained from the respective valuesof differences Φ, Γ indicated in the table of FIG. 24, as follows:

[0416] η₁={Φ₂−Φ₁−(Σ₂−Σ₁)−f(ζ₁)}/2=[−6.4−(−6.4)−{(6.4−8.4)−6.4}−8.4]/2=0

[0417] η₂={Φ₃−Φ₂−(Σ₃−Σ₂)−f(ζ₂)}/2=[0−(−6.4)−{0−(6.4−8.4)}−(−8.4)]/2=6.4

[0418] η₃={Φ₄−Φ₂−(Σ₄−Σ₃)−f(ζ₃)}/2={0−0−{(−8.4)−0}−8.4)]/2=0

[0419] η₄={Φ₅−Φ₄−(Σ₅−Σ₄)−f(ζ₄)}/2={−6.4−0−{−6.4−(−8.4)}−(31 8.4}/2=−6.4

[0420] η₅={Φ₆−Φ₅−(Σ₆−Σ₅)−f(ζ₅ 0≡/2={0−(−6.4)−{(−8.4)−6.4}−8.4}/2=6.4

[0421] η₆={Φ₁−Φ₆−(Σ₁−Σ₇)−f(ζ₆)≡/2={−6.4−0−}6.4−(−8.4}−(−8.4)}/2=−6.4

[0422] As is apparent from the above results, one or more cylinderswhich has or have the value of variable η_(i) equal to 6.4 has or havethe small exhaust-valve clearance, and one or more cylinders which hasor have the number or numbers (#1 to #6) smaller than the number of theabove one cylinder or each of the above cylinders and greater than thenumber of a cylinder having the value of variable η_(i) equal to −6.4has or have the small exhaust-valve clearance. For example, if η₅=6.4,η₄=η₃=η₂=0, =−6.4, and η₆=−6.4, then the fifth, fourth, third, secondcylinders #5, #4, #3, #2 have the fault of small exhaust-valve clearanceand the first and sixth cylinders #1, #6 does not have the fault. StepU400 is followed by Step U402 to judge whether each of the six cylinders#1 to #6 has the fault of small exhaust-valve clearance based on thecorresponding value of variable η_(i) calculated for the each cylinderat Step U400. The thus made judgments are used to determine values to beset in the fault flag ‘flag_(exs)’. The above description has been madeon the assumption that the variable η_(i) can take one of 0, 6.4, and−6.4. However, in fact, the variable i falls in one of three ranges,from −2 to 2, from 2 to 10, and from −10 to −2.

[0423] In the case where it can be said that the assumption that thefault of small exhaust-valve clearance does not simultaneously occur toall the three cylinders of each one of the two banks is correct, the CPUcan judge whether the cylinder indicated by the variable ‘i’ has thefault of small exhaust-valve clearance, based on a variable, ΔΔΦ_(i),defined by the following expression (19):

ΔΔΦ_(i)=ΔΦ_(i)+ΔΦ_(i+1)−2·ΔΦ_(m)  (19)

[0424] Since the variable ΔΔΦ_(i) is obtained based on the sum of thevalue of relative difference ΔΦ_(i) when the variable ‘i’ is an oddnumber and the value of relative difference ΔΦ_(i) when the variable ‘i’is an even number, the influences which may result from the faults withthe cam pulleys 24, 26 and the driven gears 40, 42 are offset.Therefore, the variable ΔΔΦ_(i) is influenced by only the fault of smallexhaust-valve clearance.

[0425] The following expression (20) is obtained by replacing, in theexpression (19), the relative differences ΔΦ_(i), ΔΦ_(i+1) with thosedefined by the expression (13):

ΔΔΦ_(i)=Φ_(i+2)−Φ_(i)  (20)

[0426] Thus, it can be said that the test using the variable ΔΔΦ_(i) iscarried by grouping the respective values of difference Φ_(i) for allthe six cylinders #1 to #6, into a first group including the values forthe odd-numbered cylinders #1, #3, #5 and a second group including thevalues for the even-numbered cylinders #2, #4, #6, and then comparing,in each of the first and second groups, two values with each other.

[0427] The variable ΔΔΦ_(i) can be calculated according to theexpression (20), based on the value of difference Φ_(i) indicated in thetable of FIG. 24, and the thus obtained values of variable ΔΔΦ_(i) areequal to those obtained according to the expression (19) in actualengine tests. Next, there will be shown some examples calculatedaccording to the expression (20).

[0428] For example, in the case where the cylinder #1 corresponding tothe variable ‘i’=1 has the fault of small exhaust-valve clearance, thefollowing results are obtained: ΔΔΦ₁=Φ₃−Φ₁=6.4, ΔΔΦ₅=Φ₁−Φ₅=−6.4, ΔΔΦ₂(=Φ₄−Φ₂)=ΔΔΦ₃ (=Φ₅−Φ₂)=ΔΔΦ₄(=Φ₆−Φ₄)=ΔΔΦ₆ (=Φ₂−Φ₆)=0. The respectivevalues of variable ΔΔΦ_(i) for the even-numbered cylinders #2, #4, $6are all zero, which indicates that the right bank has no cylinder havingthe fault of small exhaust-valve clearance.

[0429] In addition, in the case where the cylinders #1, #3 correspondingto the variable ‘i’=1 and the variable ‘i’=3 have the fault of smallexhaust-valve clearance, the following results are obtained:ΔΔΦ₁=ΔΔΦ₂=0, ΔΔΦ₃=6.4, Φ₄=0, ΔΔΦ₅=−6.4, and ΔΔΦ₆=0.

[0430] Although no more examples are provided, in the case where it canbe assumed that the fault of small exhaust-valve clearance occurs to atmost two cylinders of each one of the two banks, one or two cylindershaving the fault of small exhaust-valve clearance can be specified basedon the pattern of respective values of variable ΔΔΦ_(i) for the threecylinders of that bank.

[0431] A similar test can be performed using a variable, ΔΔΣ_(i),(=ΔΣ_(i)+ΔΣ_(i+1)−2·ΔΣ_(m)which is calculated from the respective valuesof relative difference ΔΣ_(i). In the foregoing description, it has beenassumed that the difference Φ_(i) takes the value of −6.4 indicated inthe table of FIG. 24 when the cylinder has the fault of smallexhaust-valve clearance. However, since the difference Φ_(i) ischangeable in the range of from −2 to −10, the CPU identifies in whichone of three ranges, from −2 to 2, from 2 to 10, and from −2 to −10, thevalue of variable ΔΔΦ_(i) for each cylinder falls and, based on theobtained results, specifies one or two cylinders having the fault ofsmall exhaust-valve clearance.

[0432]FIG. 72 is a flow chart representing a cam-pulley test called atStep U206 of FIG. 68. First, at Step U500, the CPU calculates avariable, ρ_(i), for each of the six cylinders #1 to 46 which isindicated by the variable ‘i’, according to the following expression:

ρ_(i)=ΔΦ_(i)−ΔΦ_(m) −{g _(i+1)(η_(j))−g _(i)(η_(j))}  (21)

[0433] The relative difference ΔΦ_(i) is a value which is actuallyobtained, and the average relative difference ΔΦ_(m) is equal to 120degrees. The function, g_(i)(η_(j)), is employed for eliminating theinfluence of the fault of small exhaust-valve clearance that may becontained in the relative difference ΔΦ_(i). The variable η_(j) isobtained according to the expression (17). The function g_(i)(η_(j))provides −6.4 when the cylinder indicated by the variable ‘i’ has thefault of small exhaust-valve clearance; and 0 when it does not. Thesuffix, ‘j’, of the variable η_(j) is used to distinguish the variableη_(j) from the variable ρ_(i). This means that it is not possible tojudge, based on only the variable η_(i), whether the cylinder indicatedby the variable ‘i’ has the fault of small exhaust-valve clearance andthat it is possible to do so based on the respective values of variableη_(j) obtained for all the cylinders. From the above-indicatedexpression (13), it is understood that the difference, ΔΦ_(i)−ΔΦ_(m),present in the right side of the expression (21) is equal to thedifference, ΔΦ_(i+1)−ΔΦ_(i). Therefore, the expression (21) can bemodified as follows:

ρ_(i)=Φ_(i+1)−Φ_(i) −{g _(i+1)(η_(j))−g _(i)(η_(j))}  (22)

[0434] The values of variable ρ_(i), which will be exemplified later,can be calculated according to this expression (22), based on the valueof difference Φ indicated in the table of FIG. 24. However, in actualengine tests, the values of variable ρ_(i) are calculated according tothe expression (21).

[0435] The influence of the small exhaust-valve clearance that may becontained in the difference Φ_(i) or the relative difference ΔΦ_(i) ischangeable as described above. Therefore, it is preferred that the valueprovided by the function g_(i)(η_(j)) reflect the magnitude of thechangeable influence. The changeable influence may be removed by, e.g.,defining the function g_(i)(η_(j)) such that the function g_(i)(η_(j))provides a value obtained by subtracting, from the actually measuredvalue of the relative difference ΔΦ_(i), a multiple of fifteen which isthe most approximate to the measured value. The thus obtained value ofvariable ρ_(i) is one of 0, ±15, and ±30 and is free from any influenceof the faults with the exhaust-valve clearance.

[0436] Hereinafter, the value of variable ρ_(i) when the variable ‘i’ isan odd number will be indicated at ρ_(odd), and the value of variableρ_(i) when the variable ‘i’ is an even number will be indicated atρ_(even). The combination, (ρ_(odd), ρ_(even)) can take one of fivecombinations, (0, 0), (15, −15), (−15, 15), (30, −30), and (−30, 30).The five combinations correspond to the following assembled states ofthe cam pulleys 24, 26:

[0437] Combination (1)—(0, 0):

[0438] two cam pulleys 24, 26 normal, or

[0439] two cam pulleys 24, 26 one-tooth fast or slow

[0440] Combination (2)—(15, −15):

[0441] left cam pulley 24 one-tooth fast and right cam pulley 26 normal,or

[0442] left cam pulley 24 normal and right cam pulley 26 one-tooth slow

[0443] Combination (3)—(−15, 15):

[0444] left cam pulley 24 normal and right cam pulley 26 one-tooth fast,or

[0445] left cam pulley 24 one-tooth slow and right cam pulley 26 normal

[0446] Combination (4)—(30, −30):

[0447] left cam pulley 24 one-tooth fast and right cam pulley 26one-tooth slow

[0448] Combination (5)—(−30, 30):

[0449] left cam pulley 24 one-tooth slow and right cam pulley 26one-tooth fast

[0450] When the combination (ρ_(odd), ρ_(even)O is the above-indicatedfourth or fifth combination (4), (5), the CPU can completely specify therespective assembled states of the two cam pulleys 24, 26. On the otherhand, when the combination (ρ_(odd), ρ_(even)) is one of theabove-indicated first to third combinations (1), (2), (3), the CPUcannot completely specify the assembled states of the two cam pulleys24, 26. However, when the combination (ρ_(odd), ρ_(even)) is the secondor third combination (2), (3), the CPU can specify two possible cases;and when the combination (ρ_(odd), ρ_(even)) is the first combination(1), the CPU can specify the three possible cases. This information isvery useful when an operator or worker corrects the engine 90 based onthe outcome of the present test. Regarding the first combination (1), itshould be noted that the possibility that both the two cam pulleys 24,26 are one- tooth fast or slow is very low.

[0451] Step U500 is followed by Step U502 to set values in the faultflag ‘flag_(cam)’ based on the combination (ρ_(odd), ρ_(even)). When thecombination (ρ_(odd), ρ_(even)) is the first combination (1), the CPUsets 0×Cf (i.e., 11001111) in the flag ‘flag_(cam)’. As is understoodfrom FIG. 69, the values, 0×Cf, are provided by the logical sum of 0×05(00000101) indicating that the two cam pulleys 24, 26 are one-toothfast, and 0×0a (00001010) indicating that the two cam pulleys 24, 26 areone-tooth slow, and the value of 1 set in each of the error-1 anderror-2 bits of the flag ‘flag_(cam)’. Since both the error-1 anderror-2 bits have the value of 1, the lamps corresponding to the bitseach having the value of 1 are flashed as described above.Alternatively, the flag ‘flag_(cam)’ may be set to 0×80 (10000000). Whenthe combination (ρ_(odd), ρ_(even)) is the second combination (2), theCPU sets 0×C9 (i.e., 11001001) in the flag ‘flag_(cam)’. The values,0×C9, are provided by the logical sum of 0×01 (00000001) indicating thatthe left cam pulley 24 is one-tooth fast and the right cam pulley 26 isnormal, and 0×08 (00001000) indicating that the left cam pulley 24 isnormal and the right cam pulley 26 is one-tooth slow, and the value of 1set in each of the error-1 and error-2 bits of the flag ‘flag_(cam)’.

[0452] When the combination (ρ_(odd), ρ_(even)) is the third combination(3), the CPU sets 0×86 (i.e., 11000110) in the flag ‘flag_(cam)’. Thevalues, 8×86, are provided by the logical sum of 0×02 (00000010)indicating that the left cam pulley 24 is one-tooth slow and the rightcam pulley 26 is normal, and 0×04 (00000100) indicating that the leftcam pulley 24 is normal and the right cam pulley 26 is one-tooth fast,and the value of 1 set in each of the error-1 and error-2 bits of theflag ‘flag_(cam)’. When the combination (ρ_(odd), ρ_(even)) is thefourth combination (4), the CPU sets 0×09 (i.e., 00001001) in the flag‘flag_(cam)’. The values, 0×09, indicate that the left cam pulley 24 isone-tooth fast and the right cam pulley 26 is one-tooth slow. When thecombination (ρ_(odd), ρ_(even)) is the fifth combination (5), the CPUsets 0×06 (i.e., 00000110) in the flag ‘flag_(cam)’. The values, 0×06,indicate that the left cam pulley 24 is one-tooth slow and the right campulley 26 is one-tooth fast. In the case where both the error-1 anderror-2 bits of the flag ‘flag_(cam)’ have the value of 1, the lamps(FIG. 26) corresponding to the bits which are other than the error-1 anderror-2 bits in the flag and have the value of 1 are flashed undercontrol of the CPU.

[0453] The combination (ρ_(odd), ρ_(even)) obtained from one pair ofodd-numbered and even-numbered cylinders may be used alone. However, theformer combination (ρ_(odd), ρ_(even)) may be used with another or othercombinations obtained from another or other pairs of odd-numbered andeven-numbered cylinders. For example, the average of respective valuesof the variable ρ_(odd) for the three odd-numbered cylinders may becombined with the average of respective values of the variable ρ_(even)for the three even-numbered cylinders. Thus, it can be said that thecam-pulley test indicated in FIG. 72 is carried by comparing thevariable ρ_(i) of at least one odd-numbered cylinder with that of atleast one even-numbered cylinder. Otherwise, it can be said that thetest is carried out by grouping the respective values of variable ρ_(i)for all the six cylinders, into a first group including the values forthe odd-numbered cylinders and a second group including the values forthe even-numbered cylinders, and then comparing one or more values ofone of the two groups with one or more values of the other group.

[0454]FIG. 73 shows a flow chart representing theone-tooth-slow-driven-gear and intake-valve-clearance test called atStep U208 of FIG. 68. First, at Step U600, the CPU calculates avariable, λ_(i), for each of the cylinders #1 to #6 which is indicatedby the variable ‘i’, according to the following expression (23):

λ_(i)=ΔΓ_(i)−ρ_(i) −h _(i)(ζ_(j))  (23)

[0455] The function, h_(i)(ζ_(j)), is a function of the above-describedvariable ζ_(j), and is employed for eliminating the influence of theone-tooth fast state of the driven gear 40, 42 that may be contained inthe actually measured value of relative difference ΔΓ_(i). The functionh_(i)(ζ_(j)) provides 0 when both the two driven gears 40, 42 areone-tooth fast, or when neither of the two driven gears 40, 42 isone-tooth fast; 18 when one of the driven gears 40, 42 which correspondsto the cylinder indicated by the variable ‘i’ is one-tooth fast; and −18when one of the driven gears 40, 42 which does not correspond to thecylinder indicated by the variable ‘i’ is one-tooth fast. The reason whynot the suffix ‘i’ but the suffix ‘j’ is used for the variable ζ_(j) isthat it is not possible to specify, based on only the value of variableζ_(i) for the cylinder indicated by the variable ‘i’, whether one of thedriven gears 40, 42 which corresponds to that cylinder is one-tooth fastand that it is possible to do so based on the combination (ζ_(odd),ζ_(even)) according to the test indicated in FIG. 70. The influence ofthe one-tooth fast or HER slow state of the cam pulley 24, 26 can beremoved by subtracting the variable ρ_(i) from the relative differenceΔΓ_(i).

[0456] The variable λ_(i) calculated according to the expression (23) isfree from the influences of the above-indicated faults and may containthe influences of the one-tooth slow state of the driven gear 40, 42and/or the small or large state of the intake-valve clearance. Thefollowing expression (24) is obtained by replacing, in the expression(23), the relative difference ΔΓ_(i) with that defined by the expression(12), and transposing the term, ΔΓ_(m), from the right side to the leftside:

λ_(i)−ΔΓ_(m)=Γ_(i+1)−Γ_(i)−ρ_(i) −h _(i)(ζ_(j))  (24)

[0457] The right side of the expression (24) can be calculated based onthe value of difference Γ indicated in the table of FIG. 24. Althoughthe expression (24) is different from the expression (23) that isemployed in actual engine tests, the two expressions (23), (24) providethe same result for the same engine 90. The left side of the expression(24) (i.e., value obtained by subtracting, from the variable λ_(i), theexhaust-pressure maximal-value-angle average relative differenceΔΓ_(m)=120 degrees) falls one of the following eleven ranges (1) to(11), depending upon the presence or absence of the one-tooth-slowdriven gear and/or the small or large intake-valve clearance:

[0458] Range (1): −30≦λ_(i)−ΔΓ_(m)<−20

[0459] Range (2): −20≦λ_(i)−ΔΓ_(m)<−16

[0460] Range (3): −16≦λ_(i)−ΔΓ_(m)<−12

[0461] Range (4): −12≧λ_(i)−ΔΓ_(m)<−6

[0462] Range (5): −6≦λ_(i)−ΔΓ_(m)<−2

[0463] Range (6): −2≦λ_(i)−ΔΓ_(m)<2

[0464] Range (7): 2≦λ_(i)−ΔΓ_(m)<6

[0465] Range (8): 6≦λ_(i)−ΔΓ_(m)<12

[0466] Range (9): 12≦λ_(i)−ΔΓ_(m)<16

[0467] Range (10): 16≦λ_(i)−ΔΓ_(m)<20

[0468] Range (11): 20≦λ_(i)−ΔΓ_(m)<30

[0469]FIG. 74 shows the above eleven ranges (1) to (11). The one-toothslow state of the driven gear 40, 42 stepwise influences the value,λ_(i)−ΔΓ_(m). The magnitude of this influence is 0 when both the twodriven gears 40, 42 are one-tooth slow, or when the two driven gears arenormal; −18 when one of the driven gears 40, 42 which corresponds to thecylinder indicated by the variable ‘i’ is one-tooth slow; and 18 whenone of the driven gears 40, 42 which does not correspond to the cylinderindicated by the variable ‘i’ is one-tooth slow.

[0470] Meanwhile, the CPU can judge that the intake-valve clearance ofeach cylinder is normal, if the difference Γ of that cylinder falls inthe range of −2 to 2. Therefore, even if it may be judged that theintake-valve clearance of one cylinder is normal, the difference Γ ofthat cylinder may take any value falling in the range of −2 to 2. Inaddition, even if the intake-valve clearance may be very small, thedifference Γ cannot be smaller than −10; and even if the intake-valveclearance may be very large, the difference Γ cannot be greater than 10.Therefore, the entire range of parameter, λ_(i)−ΔΓ_(m), is divided intothe eleven ranges (1) to (11) which are defined by the following bordervalues: −18±(10+2), −18±2, 0±(10+2), 0±2, 18±(10+2), and 18±2.

[0471] Each of the above eleven ranges (1) to (11) corresponds to thefollowing fault or faults with one of the two driven gears 40, 42 whichcorresponds to the cylinder indicated by the variable ‘i’ and/or theother gear which does not corresponds to the same cylinder, and with theintake-valve clearance of the same cylinder:

[0472] Range (1): the one of driven gears 40, 42 one-tooth slow, andintake-valve clearance large

[0473] Range (2): the one of driven gears 40, 42 one-tooth slow, andintake-valve clearance normal

[0474] Range (3): the one of driven gears 40, 42 one-tooth slow, andintake-valve clearance small

[0475] Range (4): the one of driven gears 40, 42 one-tooth slow, andintake valve clearance small, or

[0476]  both driven gears 40 and 42 normal, and intake-valve clearancelarge, or

[0477]  both driven gears 40 and 42 one-tooth slow, and intake-valveclearance large

[0478] Range (5): both driven gears 40 and 42 normal, and intake-valveclearance large, or

[0479]  both driven gears 40 and 42 one-tooth slow, and intake-valveclearance large

[0480] Range (6): both driven gears 40 and 42 normal, and intake-valveclearance normal, or

[0481]  both driven gears 40 and 42 one-tooth slow, and intake-valveclearance normal

[0482] Range (7): both driven gears 40 and 42 normal, and intake-valveclearance small, or

[0483]  both driven gears 40 and 42 one-tooth slow, and intake-valveclearance small

[0484] Range (8): both driven gears 40 and 42 normal, and intake-valveclearance small, or

[0485]  both driven gears 40 and 42 one-tooth slow, and intake-valveclearance small, or

[0486]  the other of driven gears 40, 42 one-tooth slow, andintake-valve clearance large

[0487] Range (9): the other of driven gears 40, 42 one-tooth slow, andintake-valve clearance large

[0488] Range (10): the other of driven gears 40, 42 one-tooth slow, andintake-valve clearance normal

[0489] Range (11): the other of driven gears 40, 42 one-tooth slow, 24and intake-valve clearance small

[0490] When the value, λ_(i)−ΔΓ_(m), falls in one of the first to thirdranges (1) to (3) and ninth to eleventh ranges (9) to (11), the CPU canspecify the assembled state (i.e., large, normal, or small state) of theintake-valve clearance of the cylinder indicated by the variable ‘i’,and the assembled state (i.e., one-tooth slow or normal state) of one ofthe two driven gears 40, 42 which corresponds to that cylinder. On theother hand, when the value, λ_(i)−ΔΓ_(m), falls in one of the fourth toeighth ranges (4) to (8), the CPU can only specify a plurality ofcandidates for the assembled state of the intake-valve clearance of thecylinder indicated by the variable ‘i’ and the assembled state of one ofthe two driven gears 40, 42 which corresponds to that cylinder. However,even in the case where the value, λ_(i)−ΔΓ_(m), falls in one of theranges (4) to (8), the CPU may be able to specify the assembled state ofthe intake-valve clearance of the cylinder and the assembled state ofone of the two driven gears 40, 42 which corresponds to the cylinder.For example, when the value, λ_(i)−ΔΓ_(m), of one cylinder falls in theeighth range (8), the CPU can specify that the other of driven gears 40,42 which does not corresponds to the one cylinder is one-tooth slow andthe intake-valve clearance of the one cylinder is large, if the value,λ_(i)−ΔΓ_(m), of another cylinder belonging to the same bank as that towhich the above one cylinder belongs falls in the ninth range (9). Thus,the present engine testing apparatus can collect information from eachone of the two banks of the engine 90, independent of the other bank,and can collect more information about the assembled state of the engine90. Step U600 is followed by Step U602 to set values in the fault flags‘flag_(drvn)’, ‘flag_(inl)’, ‘flag_(ins)’. However, when the CPUspecifies a plurality of candidates for one or more faults, the CPU sets1 in each of the error-1 and error2 bits of corresponding one or moreflags, thereby indicating that the CPU failed to specify clearly one ormore faults with the driven gears 40, 42 and the intake valves 50 of theengine 90.

[0491]FIG. 75 is a flow chart representing alarge-exhaust-valve-clearance test called at Step U210 of FIG. 68. Thistest may not provide a correct result, if the engine 90 has another orother faults with the cam pulleys 24, 26, the driven gears 40, 42, theintake-valve clearances of the cylinders #1 to #6, etc. However, if theengine 90 has a cylinder with the fault of large exhaust-valve clearanceand does not have any other faults, the CPU can specify that cylinder.Therefore, if the fault finder 117 finds one or more faults in theabove-described prior tests, the CPU does not carry out the presentsubroutine, and concludes that whether the exhaust-valve clearance ofeach cylinder is large or not cannot be judged. In this case, the CPUsets 1 in the error-1 bit of the fault flag ‘flag_(exl)’. Accordingly,the lamps 230 corresponding to all the cylinders #1 to #6 are flashed.

[0492] In the test of FIG. 75, first, at Step U700, the CPU determines,as a variable, β_(MAX), the maximum one of the respective values ofexhaust-pressure constant-value difference β_(i) for all the cylinders#1 to #6 (i=1 to 6), and determines, as a variable, β_(MIN), the minimumone of the same values. Step U700 is followed by Step U702 to judgewhether a value obtained by subtracting the variable β_(MIN) from thevariable β_(MAX) is greater than a threshold value, β_(th). If apositive judgment is made at Step U702, the control of the CPU goes toStep U704 to specify that the cylinder having the maximum differenceβ_(MAX) has the large exhaust-valve clearance, and sets 1 in one of thebits of the flag ‘flag_(exl)’ which corresponds to that cylinder. Then,the CPU quits the present subroutine. The threshold value β_(th) is aprescribed constant value. On the other hand, if a negative judgment ismade at Step U702, the CPU directly quits the present test.

[0493] The test indicated in FIG. 75 is based on the assumption that theengine 90 has at most one cylinder with the fault of large exhaust-valveclearance. Even if this assumption may not be correct, this test isuseful in the case where it can be said that the assumption that theexhaust-valve clearance of at least one cylinder is normal is correct,that is, in the case where it can be said that there is no possibilitythat the respective exhaust-valve clearances of all the cylinders belarge. In the last case, the present test is carried out for the purposeof finding one of the cylinders which has the largest exhaust-valveclearance. If the CPU finds a cylinder with the large exhaust-valveclearance in this manner, then there remains some possibility thatanother or other (but not all) cylinders may have the largeexhaust-valve clearance. In this case, the CPU may set 1 in one of thebits of the fault flag ‘flag_(exl)’ which corresponds to the cylinderjudged as having the large exhaust-valve clearance, and set 1 in theerror-1 bit of the flag. Consequently the lamp corresponding to thecylinder is lit, and the lamps corresponding to the other cylinders areflashed. Thus, the display 118 indicates that there is some possibilitythat another or other (but not all) cylinders may have the largeexhaust-valve clearance.

[0494] In the case where the possibility that all the cylinders may havethe large exhaust-valve clearance cannot completely be negated, the CPUcommands the display 118 to indicate the above situation, even if thetest of FIG. 75 may show that all the cylinders are normal. Therefore,when the test of FIG. 75 shows that all the cylinders are normal, theCPU may set 1 in the error-1 bit of the flag ‘flag_(exl)’ and set 0 ineach of the first to sixth bits of the flag, thereby indicating thatthere is some possibility that all the cylinders may have the largeexhaust-valve clearance. In this case, the lamps 230 corresponding toall the cylinders are flashed.

[0495]FIG. 76 is a flow chart representing anotherlarge-exhaust-valve-clearance test which may be called in place of thetest of FIG. 75 at Step U210 of FIG. 68. This test is based on thecomparison between the value of difference β_(i) obtained for eachcylinder #1 to #6 and the average of the respective values of differenceβ_(i) obtained for all the cylinders. First, at Step U800, the CPUdetermines, as a variable, β_(MEAN), the average of respective values ofdifference β_(i) obtained for all the cylinders. Step U800 is followedby Step U802 to judge whether a value obtained by subtracting thevariable B MEAN from the value of difference β_(i) for the currentcylinder indicated by the variable ‘i’ is greater than a thresholdvalue, β_(th), (i.e., a prescribed constant value). If a positivejudgment is made at Step U802, the control of the CPU goes to Step U804to specify that the cylinder or cylinders satisfying the above conditionhas or have the large exhaust-valve clearance, and sets 1 in one or moreof the bits of the fault flag ‘flag_(exl)’ which corresponds orcorrespond to that cylinder or those cylinders. Then, the CPU quits thepresent subroutine. On the other hand, if a negative judgment is made atStep U802, the CPU directly quits the present test. This test is basedon the assumption that the engine 90 has at most a small number ofcylinders (i.e., one or two cylinders) which have the fault of largeexhaust-valve clearance. Therefore, in the case where there is somepossibility that this assumption may not be correct, it is preferred tocarry out one of the two modified tests which have additionally beendescribed in association with the description of the test of FIG. 75.

[0496]FIG. 77 is a flow chart representing yet anotherlarge-exhaust-valve-clearance test which may be called in place of thetest of FIG. 75 or FIG. 76 at Step U210 of FIG. 68. This test is carriedout by grouping the respective values of difference β_(i) obtained forall the cylinders #1 to #6, into two groups, and comparing the values ofthe first group with those of the second group. First, at Step U900, theCPU arranges the respective values of difference β_(i) for all thecylinders, in the order from the maximum value to the minimum value, anddetermines, as a variable, Δβ_(k), the difference between each pair ofsuccessive values in this order. The variable Δβ_(k) takes five valueswhen the suffix ‘k’ thereof takes 1 to 5, respectively. Step U900 isfollowed by Step U902 to determine, as a variable Δβ_(MAX), the maximumone of the five values which are taken by the variable Δβ_(k).Subsequently, at Step U904, the CPU judges whether the variable Δβ_(MAX)is greater than a threshold value, D_(th). The threshold value D_(th)may be a value which is smaller than the smaller one (hereinafter,referred to as the value β_(S); and the larger one will be referred toas the value β_(L)) of the two values β_(i) used for calculating thevariable β_(MAX) and which is determined by taking the inevitablechanges of difference β on the normal cylinders into account. If apositive judgment is made at Step U904, the control of the CPU goes toStep U906 to judge that one or more cylinders having the value ofdifference β_(i) not smaller than the value β_(L) has or have the largeexhaust-valve clearance, and sets 1 in one or more bits of the faultflag ‘flag_(exl)’ which corresponds or correspond to that cylinder orthose cylinders. Then, the CPU quits the present subroutine. On theother hand, if a negative judgment is made at Step U904, the CPUdirectly quits the present test.

[0497] If the variable Δβ_(MAX) obtained from the respective values ofdifference β_(i) for all the cylinders is greater than the thresholdvalue D_(th) also obtained based on the same values, it can be judgedthat a cylinder or cylinders having a value β_(i) not smaller than thevalue β_(L), and a cylinder or cylinders having a value β_(i) notgreater than the value β_(S), provide different groups, respectively.The CPU judges that the cylinder or cylinders having the value β_(i) notsmaller than the value β_(L), that is, the cylinder or cylinders of thefirst group has or have the fault of large exhaust-valve clearance. Thetest of FIG. 77 is based on the assumption that the inevitable changesof difference β_(i) on the normal cylinders is very small. However, inthe case where this assumption may not be correct, it is preferred tocarry out the test of FIG. 75 or FIG. 76 or a differentlarge-exhaust-valve-clearance test.

[0498] In the test of FIG. 77, the CPU judges whether each cylinder hasthe large exhaust-valve clearance or not, based on the variable Δβ_(k),the variable Δβ_(MAX), the threshold value D_(th), etc. obtained fromthe respective values of difference β_(i) for all the cylinders. Thismanner is advantageous because the threshold value D_(th) does not needany adjustment which would otherwise be needed.

[0499] Each one of the three tests of FIGS. 75, 76, and 77 may becarried out independent of the other tests. However, two or all of thosetests may be carried out in succession. In the latter case, the resultobtained from one test may differ from that or those obtained from theother test, or the other tests. The CPU may be adapted to judge,regarding one or more cylinders which is or are judged as having thelarge exhaust-valve clearance in at least one of those tests, that thereis some possibility that the fault of large exhaust-valve clearance mayhave occurred to the cylinder or cylinders.

[0500]FIG. 78 is a flow chart representing the compression-ring-missingtest called at Step U212 of FIG. 68. This test may not provide a correctresult, if the engine 90 has another or other faults with the campulleys 24, 26, the driven gears 40, 42, the intake-valve clearances ofthe cylinders #1 to #6, etc. However, if the engine 90 has a cylinderwith the fault of compression-ring missing and does not have any otherfaults, the CPU can specify that cylinder. Therefore, if the faultfinder 117 finds one or more faults in the above-described prior tests,the CPU does not carry out the present test, and concludes that whethereach cylinder has the fault of compression-ring missing cannot bejudged. In this case, the CPU sets 1 in the error-1 bit of the faultflag ‘flag_(ring)’, and sets 0 in the bits of the flag which correspondto all the cylinders #1 to #6. Accordingly, the lamps 232 correspondingto all the cylinders #1 to #6 are flashed.

[0501] In the test of FIG. 78, first, at Step U1000, the CPU determines,as a variable, , the maximum one of the respective values ofexhaust-pressure maximal-value difference α_(i) for all the cylinders #1to #6, and determines, as a variable, α_(MIN), the minimum one of thesame values. Step U1000 is followed by Step U1002 to judge whether avalue obtained by subtracting the variable α_(MIN) from the variableΔ_(MAX) is greater than a threshold value, α_(th). If a positivejudgment is made at Step U1002, the control of the CPU goes to StepU1004 to specify that the cylinder having the minimum difference α_(MIN)has the fault of compression-ring missing, and sets 1 in one of the bitsof the flag ‘flag_(ring)’ which corresponds to that cylinder. Then, theCPU quits the present subroutine. The threshold value α_(th) is aprescribed constant value. On the other hand, if a negative judgment ismade at Step U1002, the CPU directly quits the present test.

[0502] The test indicated in FIG. 78 is based on the assumption that theengine 90 has at most one cylinder with the fault of compression-ringmissing. Even if this assumption may not be correct, this test is usefulin the case where it can be said that the assumption that thecompression ring of at least one cylinder is normal is correct, that is,in the case where it can be said that there is no possibility that allthe cylinders may have the fault of compression-ring missing. In thelast case, the present test is carried out for the purpose of findingone of the cylinders which has the compression-ring missing. If the CPUfinds a cylinder with the compression-ring missing in this manner, thenthere remains some possibility that another or other (but not all)cylinders may have the same fault. Accordingly, the CPU sets 1 in one ofthe bits of the flag ‘flag_(ring)’ which corresponds to the cylinderjudged as having the compression-ring missing, and sets 1 in the error-1bit of the flag. Consequently the lamp 232 corresponding to the cylinderis lit, and the lamps 232 corresponding to the other cylinders areflashed. Thus, the display 118 indicates that there is some possibilitythat another or other (but not all) cylinders may have the fault ofcompression-ring missing.

[0503] In the case where the possibility that all the cylinders may havethe fault of compression-ring missing cannot completely be negated, theCPU commands the display 118 to indicate the above situation, even ifthe test of FIG. 78 may show that all the cylinders are normal.

[0504] Therefore, when the test of FIG. 78 shows that all the cylindersare normal, the CPU may set 1 in the error-1 bit of the flag‘flag_(ring)’ and set 0 in each of the first to sixth bits of the flag,thereby indicating that there is some possibility that all the cylindersmay have the fault of compression-ring missing. In this case, the lamps232 corresponding to all the cylinders are flashed.

[0505] As is apparent from the above description, the test of FIG. 78 isobtained by modifying the test of FIG. 75 in such a manner that thedifference β_(i) of FIG. 75 is replaced with the difference α_(i) ofFIG. 78, the threshold value β_(th) at Step U702 of FIG. 75 is replacedwith the threshold value α_(th) at Step U1002 of FIG. 78, and Step U1004of FIG. 78 is obtained by modifying Step U704 of FIG. 75. Similarly,another or other compression-ring-missing tests can be obtained bymodifying the test of FIG. 76 and/or the test of FIG. 77. In the lattercase, in addition to the same modifications as the above-indicatedmodifications to the test of FIG. 75, Step U802 of FIG. 76 is modifiedso that the CPU judges whether a value obtained by subtracting, from thevariable α_(MEAN) (corresponding to the variable β_(MEAN)), the value ofdifference α_(i) for the cylinder indicated by the variable ‘i’ isgreater than the threshold value α_(th), and Step U906 of FIG. 77 ismodified so that the CPU judges that one or more cylinders having thevalue of difference α_(i) not greater than the value as (correspondingto the value β_(S)) has or have the fault of compression-ring missing.

[0506] Subsequently, the complementary operation carried out at StepU214 of FIG. 68 will be described. At this step, the CPU sets 1 in theerror-1 bit of the fault flag ‘flag_(crnk)’. In the present faultspecifying routine, no test is performed for specifying the one-toothfast or slow state of the crank pulley 24, 26. Therefore, if a negativejudgment is made at Step U112, there is always possibility that theengine 90 may have the one-tooth fast or slow state of the crank pulley24, 26. Based on the value of 1 set in the error-1 bit of the flag‘flag_(crnk)′’, the display 118 indicates the above situation.

[0507] Next, there will be described a seventh embodiment of the presentinvention. The seventh embodiment is different from the above-describedfirst embodiment in that the engine testing routine of FIG. 25 employedin the first embodiment is replaced by a different engine testingroutine of FIG. 81 employed in the seventh embodiment. The enginetesting apparatus of FIG. 4 employed in the first embodiment is alsoemployed in the seventh embodiment, for carrying out the seventh enginetesting method in accordance with the present invention. Thus, thepresent testing apparatus can provide the table shown in FIG. 24.

[0508] The seventh engine testing method is one of methods which canspecify a single assembling fault which may have occurred to an engine90 being tested. That is, the present method is based on the assumptionthat the engine 90 has, if any, a single assembling fault as one of theabove-described thirteen faults, i.e., the one-tooth fast and slowstates of each of the cam pulleys 24, 26, the one-tooth fast and slowstates of each of the driven gears 40, 42, the small and large states ofthe intake-valve clearance, the small and large states of theexhaust-valve clearance, and the missing of the compression ring, andalso based on the assumption that each of the small and large states ofthe intake-valve clearance, the small and large states of theexhaust-valve clearance, and the missing of the compression ring doesnot simultaneously occur to two or more of the six cylinders #1 to #6 ofthe engine 90. In the present testing method, no test is carried out forfinding any faults with the crank pulley 18.

[0509] Each of the above-described thirteen faults can be identified orspecified based on respective values of exhaust-pressure maximal-valuefinite difference, δP_(EXmaxi), exhaust-pressure constant-value finitedifference, δP_(EXconsti), exhaust-pressure maximal-value-angle finiterelative difference, δΓ_(i), exhaust-pressure constant-start-anglefinite relative difference, δΣ_(i), exhaust-pressuredecrease-start-angle finite relative difference, δΦ_(i), intake-pressuremaximal-value-angle finite relative difference, δΛ_(i), andintake-pressure increase-start-angle finite relative difference, δΨ_(i),which are obtained for each of the six cylinders #1 to #6. The suffix‘i’ of each of the respective symbols δP_(EXmaxi), δP_(EXconsti),δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i) of the above-indicated sevenparameters changes to 1 to 6 corresponding to the first to sixthcylinders #1 to #6, respectively. The respective values of seventhparameters δP_(EXmaxi), δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i),δΨ_(i) for each cylinder #1 to #6 are calculated based on the respectivevalues of exhaust-pressure maximal value P_(EXmaxi), exhaust-pressureconstant value P_(EXconsti), exhaust-pressure maximal-value-anglerelative difference ΔΓ_(i), exhaust-pressure constant-start-anglerelative difference ΔΣ_(i), exhaust-pressure decrease-start-anglerelative difference ΔΦ_(i), intake-pressure maximal-value-angle relativedifference ΔΛ_(i), and intake-pressure increase-start-angle relativedifference ΔΨ_(i) which are obtained for the each cylinder, according tothe following seven expressions (25), (26), (27), (28), (29), (30), and(31), respectively:

δP_(EXmaxi)=P_(EXmaxi+1)−P_(EXmaxi)  (25)

δP_(EXconsti)=P_(EXconsti+1)−P_(EXconsti)   (26)

δΓ_(i)=ΔΓ_(i)−ΔΓ_(m)   (27)

δΣ_(i)=ΔΣ_(i)−ΔΣ_(m)  (28)

δΦ_(i)=δΦ_(i)=δΦ_(m)  (29)

δΛ_(i)=ΔΛ_(i)−ΔΛ_(m)  (30)

δΨ_(i)=ΔΨ_(i)−ΔΨ_(m)  (31)

[0510] The intake-pressure maximal-value-angle relative differenceΔΛ_(i) and the intake-pressure increase-start-angle relative differenceΔΨ_(i) which are present in the expressions (30), (31) are calculatedaccording to the following expressions (32), (33), respectively:

ΔΛ_(i)=ΔΛ_(m)+Λ_(i+1)−Λ_(i)  (32)

ΔΨ_(i)=ΔΨ_(m)+Ψ_(i+1)−Ψ_(i)  (330

[0511] In addition, the intake-pressure maximal-value-angle averagerelative difference ΔΛ_(m) and the intake-pressure increase-start-angleaverage relative difference ΔΨ_(m) which are present in the expressions(30), (31) are equal to 120 degrees. It is noted that in the followingdescription, when the number, i+1, exceeds six, the number is replacedby a number smaller by six.

[0512] In actual engine tests, the respective values of above-indicatedseven parameters δP_(EXmaxi), δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i),δΛ_(i), δΨ_(i) are calculated according to the expressions (25) to (31),respectively. However, in the following description in which the valuesindicated in the table of FIG. 24 are utilized, the seven parameters arecalculated according to the following seven expressions (34), (35),(36), (37), (38), (39), and (40), respectively, in place of theexpressions (25) to (31):

δP_(EXmaxi)=α_(i+1)−α_(i)  (34)

δP_(EXconsti)=β_(i+1)−β_(i)  (35)

δΓ_(i)=Γ_(i+1)−Γ_(i)  (36)

δΣ_(i)=Σ_(i+1)−Σ_(i)  (37)

δΦ_(i)=Φ_(i+1)−Φ_(i)  (38)

δΛ_(i)=Λ_(i+1)−Λ₈  (39)

δΨ_(i)=Ψ_(i+1)−Ψ_(i)  (40)

[0513] The respective values of the terms on the right side of each ofthe expressions (34) to (40) are indicated in the table of FIG. 24. Thatis, the same values as those calculated according to the expressions(25) to (31) in actual engine tests can be calculated based on the tableof FIG. 24 according to the expressions (34) to (40). For example, whenthe value of exhaust-pressure maximal value P_(EXmax) obtained from anormal engine is expressed as P_(EXmaxSTD), the following expressions(41), (42) are obtained:

α_(i)=P_(EXmaxi)−P_(EXmaxSTD)   (41)

α_(i+1)=P_(EXmaxi+1)−P_(EXmaxSTD)  (42)

[0514] The expression (34) is obtained by substituting, in theexpression (25), the terms, P_(EXmaxi) and P_(EXmaxi+1), with thosedefined in the expressions (41), (42). That is, the expression (25) isequivalent to the expression (34). Similarly, regarding the finitedifference δP_(EXconsti), it can easily be concluded that the expression(26) is equivalent to the expression (35). In addition, the fiveexpressions (36) to (40) are obtained by substituting, in the fiveexpressions (27) to (31), the terms, ΔΓ_(i), ΔΣ_(i), ΔΦ_(i), ΔΛ_(i),ΔΨ_(i), with those defined by the expressions (27) to (31), (32) and(33). Accordingly, values which will be exemplified below are obtainedin the calculating manners different from those in which values areobtained according to the expressions (25) to (31) in actual enginetests. However, the values obtained according to the expressions (34) to(40) are equal to those obtained according to the expressions (25) to(31), and the former values are calculated from the values indicated inthe table of FIG. 24. Thus, the values obtained according to theexpressions (34) to (40) can be used as the values obtained according tothe expressions (25) to (31) in actual engine tests.

[0515] First, the manner in which each of the one-tooth fast and slowstates of the cam pulleys 24, 26 and the one-tooth fast and slow statesof the driven gears 40, 42 is identified or specified will be describedbelow.

[0516] In the case where the engine 90 has either the one-tooth faststate of the left cam pulley 24 of the left bank or the one-tooth slowstate of the right cam pulley 26 of the right bank, the respectivevalues of above-indicated seven parameters δP_(EXmaxi), δP_(EXconsti),δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i) are calculated according to theexpressions (34) to (40), as follows:

[0517] δP_(EXmaxodd)=α_(even)−α_(odd)=0−(−170=17

[0518] δP_(Exmaxeven)=α_(odd)−α_(even)=−17−0=−17

[0519] δP_(EXconstodd)=β_(even)−β_(odd)=0−0=0

[0520] δP_(EXconsteven)=β_(odd)−β_(even)=0−0=0

[0521] δΓ_(odd)=Γ_(even)−Γ_(odd)=0−(−15)=15

[0522] δΓ_(even)=Γ_(odd)−Γ_(even)=−15−0=−15

[0523] δΣ_(odd)=Σ_(even)−Σ_(odd)=0−(−15)=15

[0524] δΣ_(even)=Σ_(odd)−Σ_(even)=−15−0=−15

[0525] δΦ_(odd)=Φ_(even)−Φ_(odd)=0−(−15)=15

[0526] δΦ_(even)=Φ_(odd)−Φ_(even)=−15−0=−15

[0527] δΛ_(odd)=Λ_(even)−Λ_(odd)=0−(−14)=14

[0528] δΛ_(even)=Λ_(odd)−Λ_(even)=−14−0=−14

[0529] δΨ_(odd)=Ψ_(even)−Ψ_(odd)=0−(−150=15

[0530] δΨ_(even)=Ψ_(odd)−Ψ_(even)=−15−0=−15

[0531] In the above calculations, the suffix “odd” indicates the casewhere the variable ‘i’ takes an odd number and the suffix “even”indicates the case where the variable ‘i’ takes an even number. Theabove calculations relate to the case where the engine 90 has theone-tooth fast state of the left cam pulley 24. However, the sameresults are obtained also in the case where the engine 90 has theone-tooth slow state of the right cam pulley 26.

[0532] In the case where the engine 90 has either the one-tooth slowstate of the left cam pulley 24 or the one-tooth fast state of the rightcam pulley 26, the respective values of seven parameters δP_(EXmaxi),δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i) are calculatedaccording to the expressions (34) to (40), as follows:

[0533] δP_(EXmaxodd)=α_(even)−α_(odd)=0−−17=−17

[0534] δP_(Exmaxeven)=α_(odd)−α_(even)=17−0=17

[0535] δP_(EXconstodd)=β_(even)−β_(odd)=0−0=0

[0536] δP_(EXconsteven)=β_(odd)−β_(even)=0−0=0

[0537] δΓ_(odd)=Γ_(even)−Γ_(odd)=0−15=−15

[0538] δΓ_(even)=Γ_(odd)−Γ_(even)=15−0=15

[0539] δΣ_(odd)=Σ_(even)−Σ_(odd)=0−15)=−15

[0540] δΣ_(even)=Σ_(odd)−Σ_(even)=15−0=15

[0541] δΦ_(odd)=Φ_(even)−Φ_(odd)=0−15=−15

[0542] δΦ_(even)=Φ_(odd)−Φ_(even)=15−0=15

[0543] δΛ_(odd)=Λ_(even)−Λ_(odd)=0−14=−14

[0544] δΛ_(even)=Λ_(odd)−Λ_(even)=14−0=14

[0545] δΨ_(odd)=Ψ_(even)−Ψ_(odd)=0−15=−15

[0546] δΨ_(even)=Ψ_(odd)−Ψ_(even)=15−0=15

[0547] The above calculations relate to the case where the engine 90 hasthe one-tooth slow state of the left cam pulley 24. However, the sameresults are obtained also in the case where the engine 90 has theone-tooth fast state of the right cam pulley 26.

[0548] In the case where the engine 90 has the one-tooth fast state ofthe left driven gear 40 of the left bank, the respective values of sevenparameters δP_(EXmaxi), δP_(Exconsti), δθ_(i), δΣ_(i), δΦ_(i), δΛ_(i),δΨ_(i) are calculated according to the expressions (34) to (40), asfollows:

[0549] δP_(EXmaxodd)=α_(even)−α_(odd)=0−(−42)=42

[0550] δP_(Exmaxeven)=α_(odd)−α_(even)=−42−0=−42

[0551] δP_(EXconstodd)=β_(even)−β_(odd)=0−(−100=10

[0552] δP_(EXconsteven)=β_(odd)−β_(even)=−10−0=−10

[0553] δΓ_(odd)=Γ_(even)−Γ_(odd)=0−(−18)=18

[0554] δΓ_(even)=Γ_(odd)−Γ_(even)=−18−0=−18

[0555] δΣ_(odd)=Σ_(even)−Σ_(odd)=0−(−8.4)=8.4

[0556] δΣ_(even)=Σ_(odd)−Σ_(even)=−8.4−0=−8.4

[0557] δΦ_(odd)=Φ_(even)−Φ_(odd)=0−0=0

[0558] δΦ_(even)=Φ_(odd)−Φ_(even)=0−0=0

[0559] δΛ_(odd)=Λ_(even)−Λ_(odd)=0−(−17)=17

[0560] δΛ_(even)=Λ_(odd)−Λ_(even)=−17−0=−17

[0561] δΨ_(odd)=Ψ_(even)−Ψ_(odd)=0−(−18)=18

[0562] δΨ_(even)=Ψ_(odd)−Ψ_(even)=−18−0=−18

[0563] In the case where the engine 90 has the one-tooth slow state ofthe left driven gear 40, the respective values of seven parametersδP_(Exmaxi), δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i) arecalculated according to the expressions (34) to (40), as follows:

[0564] δP_(EXmaxodd)=α_(even)−α_(odd)=0−42=−42

[0565] δP_(Exmaxeven)=α_(odd)−α_(even)=42−0=42

[0566] δP_(EXconstodd)=β_(even)−β_(odd)=0−36=36

[0567] δP_(EXconsteven)=β_(odd)−β_(even)=36−0=36

[0568] δΓ_(odd)=Γ_(even)−Γ_(odd)=0−18=18

[0569] δΓ_(even)=Γ_(odd)−Γ_(even)=18−0=18

[0570] δΣ_(odd)=Σ_(even)−Σ_(odd)=0−0=0

[0571] δΣ_(even)=Σ_(odd)−Σ_(even)=0−0=0

[0572] δΦ_(odd)=Φ_(even)−Φ_(odd)=0−0=0

[0573] δΦ_(even)=Φ_(odd)−Φ_(even)=0−0=0

[0574] δΛ_(odd)=Λ_(even)−Λ_(odd)=0−17=17

[0575] δΛ_(even)=Λ_(odd)−Λ_(even)=17−0=17

[0576] δΨ_(odd)=Ψ_(even)−Ψ_(odd)=0−18=−18

[0577] δΨ_(even)=Ψ_(odd)−Ψ_(even)=18−0=18

[0578] In the case where the engine 90 has the one-tooth fast state ofthe right driven gear 42 of the right bank, the respective values ofseven parameters δP_(EXmaxi), δP_(Exconsti), δΓ_(i), δΣ_(i), δΦ_(i),δΨ_(i), δΨ_(i) are calculated according to the expressions (34) to (40),as follows:

[0579] δP_(EXmaxodd)=α_(even)−α_(odd)=0−42=−42

[0580] δP_(Exmaxeven)=α_(odd)−α_(even)=42−0=42

[0581] δP_(EXconstodd)=β_(even)−β_(odd)=−10−0=−10

[0582] δP_(EXconsteven)=β_(odd)−β_(even)=0−(−10)=10

[0583] δΓ_(odd)=Γ_(even)−Γ_(odd)=0−18=−18

[0584] δΓ_(even)=Γ_(odd)−Γ_(even)=18−0=18

[0585] δΣ_(odd)=Σ_(even)−Σ_(odd)=−8.4−0=−8.4

[0586] δΣ_(even)=Σ_(odd)−Σ_(even)=0−(−8.4)=8.4

[0587] δΦ_(odd)=Φ_(even)−Φ_(odd)=0−0=0

[0588] δΦ_(even)=Φ_(odd)−Φ_(even)=0−0=0

[0589] δΛ_(odd)=Λ_(even)−Λ_(odd)=0−17=−17

[0590] δΛ_(even)=Λ_(odd)−Λ_(even)=17−0=17

[0591] δΨ_(odd)=Ψ_(even)−Ψ_(odd)=0−18=−18

[0592] δΨ_(even)=Ψ_(odd)−Ψ_(even)=18−0=18

[0593] In the case where the engine 90 has the one-tooth slow state ofthe right driven gear 42, the respective values of seven parametersδP_(EXmaxi), δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΨ_(i), δΨ_(i) arecalculated according to the expressions (34) to (40), as follows:

[0594] δP_(EXmaxodd)=α_(even)−α_(odd)=42−0=42

[0595] δP_(Exmaxeven)=α_(odd)−α_(even)=0−42=−42

[0596] δP_(EXconstodd)=β_(even)−β_(odd)=36−0=36

[0597] δP_(EXconsteven)=β_(odd)−β_(even)=0−36=−36

[0598] δΓ_(odd)=Γ_(even)−Γ_(odd)=18−0=18

[0599] δΓ_(even)=Γ_(odd)−Γ_(even)=0−18=−18

[0600] δΣ_(odd)=Σ_(even)−Σ_(odd)=0−0=0

[0601] δΣ_(even)=Σ_(odd)−Σ_(even)=0−0=0

[0602] δΦ_(odd)=Φ_(even)−Φ_(odd)=0−0=0

[0603] δΦ_(even)=Φ_(odd)−Φ_(even)=0−0=0

[0604] δΛ_(odd)=Λ_(even)−Λ_(odd)=17−0=17

[0605] δΛ_(even)=Λ_(odd)−Λ_(even)=0−17=−17

[0606] δΨ_(odd)=Ψ_(even)−Ψ_(odd)=18−0=18

[0607] δΨ_(even)=Ψ_(odd)−Ψ_(even)=0−18=−18

[0608]FIG. 79 shows a table representing the relationship between eachof the above-indicated eight faults and the thus obtained values ofseven parameters δP_(EXmaxi), δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i),δΛ_(i), δΨ_(i) which are equal to those calculated according to theexpressions (25) to (31). The parameter, δ(θ−Φ)_(i), indicated in thetable of FIG. 79 is defined by the following expression (43):

δ(Γ−Φ)_(i)=Δθ_(m)−ΔΦ_(m)−(ΔΓ_(i)−ΔΦ_(i))=ΔΦ_(i)−ΔΓ_(i)   (43)

[0609] In the expression (43), that the average relative differencesΔΓ_(m), ΔΦ_(m) are equal to 120 degrees are utilized. The followingexpression (44) is obtained by substituting, in the expression (43), theterms ΔΓ_(i), ΔΦ_(i) with those defined by the expressions (12), (13),respectively:

δ(Γ−Φ)_(i)=Γ_(i)−Φ_(i)−(Γ_(i+1)−Φ_(i+1))  (44)

[0610] The values of parameter δ(θ−Φ)_(i) indicated in the table of FIG.79 are not those calculated according to the expression (43) but thosecalculated according to the expression (44) using the values indicatedin the table of FIG. 24. In actual engine tests, the values of parameterδ(Γ−Φ)_(i) calculated according to the expression (43) are used. As isapparent from the expression (43) and the table of FIG. 79, theparameter δ(Γ−Φ)_(i) is equal to a parameter, δ(Ψ−Φ)_(i). Hence, theparameter δ(Γ−Φ)_(i) may be replaced by the parameter δ(Ψ−Φ)_(i).

[0611]FIG. 79 shows that the combination of respective left-bank-relatedand right-bank-related values of eight parameters δP_(EXmaxi),δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i) which areδ(Γ−Φ)_(i), that is, the pattern of sixteen finite-difference values,for each one of the eight faults is different from those for the otherfaults, except that the pattern for the one-tooth fast state of the leftcam pulley 24 is equal to that for the one-tooth slow state of the rightcam pulley 26 and that the pattern for the one-tooth slow state of theleft cam pulley 24 is equal to that for the one-tooth fast in state ofthe right cam pulley 26. Thus, for example, the one-tooth fast or slowstate of the left or right driven gear 40, 42 can be identified orspecified from the other faults. However, the one-tooth fast state ofthe left cam pulley 24 and the one-tooth slow state of the right campulley 26 cannot be identified from each other, and the one-tooth slowstate of the left cam pulley 24 and the one-tooth fast state of theright cam pulley 26 cannot be identified from each other.

[0612] Next, the manner in which each of the small and large states ofthe intake-valve clearance, the small and large states of theexhaust-valve clearance, and the missing of the compression ring isspecified will be described below.

[0613] In the case where only one cylinder #i of the engine 90 has thesmall intake-valve clearance, the respective values δP_(EXmaxi),δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ)_(i) forthat one cylinder #i that should be equal to those calculated accordingto the expressions (25) to (31) are calculated according to theexpressions (34) to (40) and (44), as follows:

[0614] δP_(EXmaxi)=α_(i+1)−α_(i)=0−(−47)=47

[0615] δP_(EXconsti)=β_(i+1)−β_(i)=0−(−160=16

[0616] δΓ_(i)=Γ_(i+1)−Γ_(i)=0−(−6.4)=6.4

[0617] δΣ_(i)=Σ_(i+1)−Σ_(i)=0−0=0

[0618] δΦ_(i)=Φ_(i+1)−Φ_(i)=0−0=0

[0619] δΛ_(i)=Λ_(i+1)−Λ_(i)=0−(−6)=6

[0620] δΨ_(i)=Ψ_(i+1)−Ψ_(i)=0−(−6.4)=6.4

[0621] δ(Γ−Φ)_(i)=Γ_(i)−Φ_(i)−(Γ_(i+1)−Φ_(i+1))

[0622]  =−6.4−0−(0−0)=−6.4

[0623] In the case where only one cylinder #i of the engine 90 has thelarge intake-valve clearance, the respective values δP_(EXmaxi),δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ)_(i) forthat one cylinder #i are calculated according to the expressions (34) to(40) and (44), as follows:

[0624] δP_(EXmaxi)=α_(i+1)−α_(i)=0−18=−18

[0625] δP_(EXconsti)=β_(i+1)−β_(i)=0−20=−20

[0626] δΓ_(i)=Γ_(i+1)−Γ_(i)=0−5.4=−5.4

[0627] δΣ_(i)=Σ_(i+1)−Σ_(i)=0−0=0

[0628] δΦ_(i)=Φ_(i+1)−Φ_(i)=0−0=0

[0629] δΛ_(i)=Λ_(i+1)−Λ_(i)=0−5=−5

[0630] δΨ_(i)=Ψ_(i+1)−Ψ_(i)=0−5.4)=−5.4

[0631] δ(Γ−Φ)_(i)=5.4−0−(0−0)=5.4

[0632] In the case where only one cylinder #i of the engine 90 has thesmall exhaust-valve clearance, the respective values δP_(EXmaxi),δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ)_(i) forthat one cylinder #i are calculated according to the expressions (34) to(40) and (44), as follows:

[0633] δP_(EXmaxi)=α_(i+1)−α_(i)=0−(−8)=8

[0634] δP_(EXconsti)=β_(i+1)−β_(i)=0−(−10)=10

[0635] δΓ_(i)=Γ_(i+1)−Γ_(i)=0−0=0

[0636] δΣ_(i)=Σ_(i+1)−Σ_(i)=0−6.4=−6.4

[0637] δΦ_(i)=Φ_(i+1)−Φ_(i)=0−(−6.4)=6.4

[0638] δΛ_(i)=Λ_(i+1)−Λ_(i)=0−0=0

[0639] δΨ_(i)=Ψ_(i+1)−Ψ_(i)=0−0=0

[0640] δ(Γ−Φ)_(i)=0−(−6.4)−(0−00=6.4

[0641] In the case where only one cylinder #i of the engine 90 has thelarge exhaust-valve clearance, the respective values δP_(EXmaxi),δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ)_(i) forthat one cylinder #i are calculated according to the expressions (34) to(40) and (44), as follows:

[0642] δP_(EXmaxi)=α_(i+1)−α_(i)=0−12=−12

[0643] δP_(EXconsti)=β_(i+1)−β_(i)=0−14=−14

[0644] δΓ_(i)=Γ_(i+1)−Γ_(i)=0−0=0

[0645] δΣ_(i)=Σ_(i+1)−Σ_(i)=0−0=0

[0646] δΦ_(i)=Φ_(i+1)−Φ_(i)=0−0=0

[0647] δΛ_(i)=Λ_(i+1)−Λ_(i)=0−0=0

[0648] δΨ_(i)=Ψ_(i+1)−Ψ_(i)=0−0=0

[0649] δ(Γ−Φ)_(i)=0−0−(0−0)=0

[0650] In the case where only one cylinder #i of the engine 90 has thecompression-ring missing, the respective values δP_(EXmaxi),δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ)_(i) forthat one cylinder #i are calculated according to the expressions (34) to(40) and (44), as follows:

[0651] δP_(EXmaxi)=α_(i+1)−α_(i)=0−(−10)=10

[0652] δP_(EXconsti)=β_(i+1)−β_(i)=0−(31 1)=1

[0653] δΓ_(i)=Γ_(i+1)−Γ_(i)=0−0=0

[0654] δΣ_(i)=Σ_(i+1)−Σ_(i)=0−0=0

[0655] δΦ_(i)=Φ_(i+1)−Φ_(i)=0−0=0

[0656] δΛ_(i)=Λ_(i+1)−Λ_(i)=0−0=0

[0657] δΨ_(i)=Ψ_(i+1)−Ψ_(i)=0−0=0

[0658] δ(Γ−Φ)_(i)=0−0−(0−0)=0

[0659]FIG. 80 shows a table representing the relationship between eachof the above-indicated five faults and the thus obtained values of eightparameters δP_(EXmaxi), δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i),δΨ_(i), δ(Γ−Φ)_(i). However, as far as the intake-valve or exhaust-valveclearance is concerned, each of those parameters changes continuously,for example, in the case where the thickness of the shim 72 shown inFIG. 3 changes among different engines 90 to be tested. Thus, the tableof FIG. 80 just exemplifies the values of eight parameters obtained whenan engine 90 has each of the faults with the intake-valve andexhaust-valve clearances. In actual engine tests, each of thoseparameters can take different values on different engines 90.

[0660] As is understood from the tables of FIGS. 79 and 80, each of theeight parameters δP_(EXmaxi), δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i),δΛ_(i), δΨ_(i), δ(Γ−Φ)_(i) takes different values for the differentassembling faults. This fact is utilized in the present engine testingmethod as described below.

[0661] Whether the engine 90 is normal is judged by judging whether allthe respective values of eight parameters δP_(EXmaxi), δP_(EXconsti),δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ)_(i) measured for eachcylinder #1 to 6# are zero. However, the measured values of thoseparameters may not be equal to zero because of measurement errors, evenif the engine 90 may be normal. In the present embodiment, a standarddeviation, σ, of each of the eight parameters is obtained, in advance,from a number of normal engines (e.g., 1,000 engines), and a referencerange for each parameter is determined as 0±3σ. If all the respectivevalues of eight parameters for each cylinder #1 to 6# falls in the eightreferences, respectively, the CPU of the fault finder 117 judges thatthe engine 90 is normal as will be described later. Usually, therespective standard deviations for the eight parameters differ from oneanother. However, in the following description, they are indicated bythe common symbol, σ, for easier understanding.

[0662] Initially, a first cam-pulley test will be described. Whether theleft cam pulley 24 of the left bank is one-tooth fast or whether theright cam pulley 26 of the right bank is one-tooth slow is judged byjudging whether all the following sixteen expressions are satisfied bythe eight values obtained for each of the odd-numbered cylinders #1, #3,#5 and the eight values obtained for each of the even-numbered cylinders#2, #4, #6 (see FIG. 79), i.e., are correct (“TRUE”):

[0663] 0+3σ<δP_(EXmaxodd)

[0664] δP_(EXmaxeven)<0−3σ

[0665] 0−3σ≦δP_(EXconstodd)≦0+3σ

[0666] 0−3σ≦δP_(EXconsteven)≦0+3σ

[0667] 0+3σ<δθ_(odd)

[0668] δΓ_(even)<0−3σ

[0669] 0+3σ<δΣ_(odd)

[0670] δΣ_(even)<0−3σ

[0671] 0+3σ<δΦ_(odd)

[0672] δΦ_(even)<0−3σ

[0673] 0+3σ<δΛ_(odd)

[0674] δΛ_(even)<0−3σ

[0675] 0+3σ<δΨ_(odd)

[0676] δΨ_(even)<0−3σ

[0677] 0−3σ≦δ(Γ−Φ)_(odd)≦0+3σ

[0678] 0−3σ≦δ(Γ−Φ)_(even)≦0+3σ

[0679] The suffix “odd” is used when the variable ‘i’ indicates an oddnumber, and the suffix “even” is used when the variable ‘i’ indicates aneven number. In the present embodiment, when the respective values ofeach parameter δP_(EXmaxodd), δP_(EXconstodd), δΓ_(odd), δΣ_(odd),δΦ_(odd), δΛ_(odd), δΨ_(odd), δ(Γ−Φ)_(odd) which are measured from allthe three cylinders #1, #3. #5 of the left bank satisfy a correspondingone of the above-indicated expressions, a positive judgment (“TRUE”) isobtained from that expression and, when the respective values of eachparameter δP_(EXmaxodd), δP_(EXconstodd), δΓ_(odd), δΣ_(odd), δΦ_(odd),δΛ_(odd), δΨ_(odd), δ(Γ−101 )_(odd) which are measured from all thethree cylinders #2, #4. #6 of the right bank satisfy a corresponding oneof the above-indicated expressions, a positive judgment (“TRUE”) isobtained from that expression.

[0680] The above-indicated sixteen expressions may be replaced by thefollowing sixteen expressions wherein the values indicated in the tableof FIG. 79 are positively utilized for specifying the faults with thecam pulleys 24, 26:

[0681] 17−3σ≦δP_(EXmaxodd)≦17+3σ

[0682] −17−3σ≦δP_(EXmaxeven)≦−17+3σ

[0683] 0−3σ≦δP_(EXconstodd)≦0+3σ

[0684] 0−3σ≦δP_(EXconsteven)023 0+3σ

[0685] 15−3σ≦δΓ_(odd)≦15+3σ

[0686] −15−3σ≦δΓ_(even)≦−15+3σ

[0687] 15−3σ≦δΣ_(odd)≦15+3σ

[0688] −15−3σ≦δΣ_(even)≦−15+3σ

[0689] 15−3σ≦δΦ_(odd)≦15+3σ

[0690] −15−3σ≦δΦ_(even)≦−15+3σ

[0691] 14−3σ≦δΛ_(odd)≦14+3σ

[0692] −14−3σ≦δΛ_(even)≦−14+3σ

[0693] 15−3σ≦δΨ_(odd)≦15+3σ

[0694] −15−3σ≦δΨ_(even)≦−15+3σ

[0695] 0−3σ≦δ(Γ−Φ)_(odd)≦0+3σ

[0696] 0−3σ≦δ(Γ−Φ)_(even)≦0+3σ

[0697] In each of other cam-pulley or driven-gear tests which will bedescribed below, a first group of expressions employed therein anddescribed therefor may be replaced by a second group of expressionssimilar to the above-indicated alternative group of expressions for thefirst cam-pulley test, though the second group of expressions are notexpressly described.

[0698] Next, a second cam-pulley test will be described. Whether theleft cam pulley 24 is one-tooth slow or whether the right cam pulley 26is one-tooth fast is judged by judging whether all the following sixteenexpressions are satisfied by the respective values of each parameterwhich are obtained for each odd-numbered cylinder #1, #3, #5 and therespective values of each parameter which are obtained for eacheven-numbered cylinder #2, #4, #6 (see FIG. 79), i.e., are correct(“TRUE”):

[0699] δP_(EXmaxodd)≦0−3σ

[0700] 0+3σ≦δP_(EXmaxeven)

[0701] 0−3σ≦δP_(EXconstodd)≦0+3σ

[0702] 0−3σ≦δP_(EXconsteven)≦0+3σ

[0703] δΓ_(odd)<0−3σ

[0704] 0+3σ≦δΓ_(even)

[0705] δΣ_(odd)<0−3σ

[0706] 0+3σ<δΣ_(even)

[0707] δΦ_(odd)<0−3σ

[0708] 0+3σ<δΦ_(even)

[0709] δΛ_(odd)<0−3σ

[0710] 0+3σ<δΛ_(even)

[0711] δΨ_(odd)<0−3σ

[0712] 0−3σ<δΨ_(even)

[0713] 0−3σ≦δ(Γ−Φ)_(odd)≦0+3σ

[0714] 0−3σ≦δ(Γ−Φ)_(even)≦0+3σ

[0715] Whether the left driven gear 40 of the left bank is one-toothfast is judged by judging whether all the following expressions aresatisfied or are correct (“TRUE”):

[0716] 0+3σ<δP_(EXmaxodd)

[0717] δP_(EXmaxeven)<0−3σ

[0718] 0+3σ<δP_(EXconstodd)

[0719] P_(EXconsteven)<0−3σ

[0720] 0+3σ<δΓ_(odd)

[0721] δΓ_(even)<0−3σ

[0722] 0+3σ<δΣ_(odd)

[0723] δΣ_(even)<0−3σ

[0724] 0−3σ≦δΦ_(odd)≦0+3σ

[0725] 0−3σ≦δΦ_(even)≦0+3σ

[0726] 0+3σ<δΛ_(odd)

[0727] δΛ_(even)<0−3σ

[0728] 0+3σ≦δΨ_(odd)

[0729] δΨ_(even)<0−3σ

[0730] δ(Γ−Φ)_(odd)<0−3σ

[0731] 0−3σ≦δ(Γ−Φ)_(even)

[0732] Whether the left driven gear 40 of the left bank is one-toothslow is judged by judging whether all the following expressions aresatisfied or are correct (“TRUE”):

[0733] δP_(EXmaxodd)<0−3σ

[0734] 0−3σ<δP_(EXmaxeven)

[0735] P_(EXconstodd)<0−3σ

[0736] 0+3σ<δP_(EXconsteven)

[0737] δΓ_(odd)<0−3σ

[0738] 0+3σ<δΓ_(even)

[0739] 0−3σ≦δΣ_(odd)≦0+3σ

[0740] 0−3σ≦δΣ_(even)≦0+3σ

[0741] 0−3σ≦δΦ_(odd)≦0+3σ

[0742] 0−3σ≦δΦ_(even)≦0+3σ

[0743] δΛ_(odd)<0−3σ

[0744] 0+3σ≦δΛ_(even)

[0745] δΨ_(odd)<0−3σ

[0746] 0+3σ<δΨ_(even)

[0747]0+3σ<δ(Γ−Φ) _(odd)

[0748] δ(Γ−Φ)_(even)<0−3σ

[0749] Whether the right driven gear 42 of the right bank is one-toothfast is judged by judging whether all the following expressions aresatisfied or are correct (“TRUE”):

[0750] δP_(EXmaxodd)<0−3σ

[0751] 0+3σ<δP_(EXmaxeven)

[0752] P_(EXconstodd)<0−3σ

[0753] 0+3σ<δP_(EXconsteven)

[0754] δΓ_(odd)<0−3σ

[0755] 0+3σ<δΓ_(even)

[0756] Σ_(odd)<0−3σ

[0757] 0+3σ<δΣ_(even)

[0758] 0−3σ≦δΦ_(odd)≦0+3σ

[0759] 0−3σ≦δΦ_(even)≦0+3σ

[0760] δΛ_(odd)<0−3σ

[0761] 0+3σ≦δΛ_(even)

[0762] δΨ_(odd)<0−3σ

[0763] 0+3σ<δΨ_(even)

[0764] 0+3σ<δ(Γ−Φ)_(odd)

[0765] δ(Γ−Φ)_(even)<0−3σ

[0766] Whether the right driven gear 42 of the right bank is one-toothslow is judged by judging whether all the following expressions aresatisfied or are correct (“TRUE”):

[0767] 0+3σ<δP_(EXmaxodd)

[0768] δP_(EXmaxeven)<0−3σ

[0769] 0+3σ<δP_(EXconstodd)

[0770] P_(EXconsteven)<0−3σ

[0771] 0+3σ<δΓ_(odd)

[0772] δΓ_(even)<0−3σ

[0773] 0−3σ≦δΣ_(odd)≦0+3σ

[0774] 0−3σ≦δΣ_(even)≦0+3σ

[0775] 0−3σ≦δΦ_(odd)≦0+3σ

[0776] 0−3σ≦δΦ_(even)≦0+3σ

[0777] 0+3σ<δΛ_(odd)

[0778] δΛ_(even)<0−3σ

[0779] 0+3σ<δΨ_(odd)

[0780] δΨ_(even)<0−3σ

[0781] δ(Γ−Φ)_(odd)<0−3σ

[0782] 0+3σ<δ(Γ−Φ)_(even)

[0783] Next, there will be described intake-valve-clearance tests.Whether the cylinder indicated by the variable ‘i’ (i=1 to 6) has thesmall intake-valve clearance is judged by judging whether all thefollowing expressions are satisfied (see FIG. 80), i.e., are correct(“TRUE”):

[0784] 0+3σ<δP_(EXmaxi)

[0785] 0+3σ<δP_(EXconsti)

[0786] 0+3σ<δΓ_(i)

[0787] 0−3σ≦δΣ_(i)≦0+3σ

[0788] 0−3σ≦δΦ_(i)≦0+3σ

[0789] 0+3σ<δΛ_(i)

[0790] 0+3σ<δΨ_(i)

[0791] δ(Γ−Φ)_(i)<0−3σ

[0792] Whether the cylinder indicated by the variable ‘i’ has the largeintake-valve clearance is judged by judging whether all the followingexpressions are satisfied (see FIG. 80), i.e., are correct (“TRUE”):

[0793] δP_(EXmaxi)<0−3σ

[0794] P_(EXconsti)<0−3σ

[0795] δΓ_(i)<0−3σ

[0796] 0−3σ≦δΣ_(i)≦0+3σ

[0797] 0−3σ≦δΦ_(i)≦0+3σ

[0798] δΛ_(i)<0−3σ

[0799] δΨ_(i)<0−3σ

[0800] 0+3σ<δ(Γ−Φ)_(i)

[0801] Next, there will be described exhaust-valve-clearance tests.Whether the cylinder indicated by the variable ‘i’ (i=1 to 6) has thesmall exhaust-valve clearance is judged by judging whether all thefollowing expressions are satisfied (see FIG. 80), i.e., are correct(“TRUE”)

[0802] 0+3σ<δP_(EXmaxi)

[0803] 0+3σ<δP_(EXconsti)

[0804] 0−3σ≦δΓ_(i)≦0+3σ

[0805] δΣ_(i)<0−3σ

[0806] 0+3σ<δΦ_(i)

[0807] 0−3σ≦δΛ_(i)≦0+3σ

[0808] 0−3σ≦δΨ_(i)≦0+3σ

[0809] 0+3σ<δ(Γ−Φ)_(i)

[0810] Whether the cylinder indicated by the variable ‘i’ has the largeexhaust-valve clearance is judged by judging whether all the followingexpressions are satisfied (see FIG. 80), i.e., are correct (“TRUE”):

[0811] δP_(EXmaxi)<0−3σ

[0812] P_(EXconsti)<0−3σ

[0813] 0−3σ≦δΓ_(i)≦0+3σ

[0814] 0−3σ≦δΣ_(i)≦0+3σ

[0815] 0−3σ≦δΦ_(i)≦0+3σ

[0816] 0−3σ≦δΛ_(i)≦0+3σ

[0817] 0−3σ≦δΨ_(i)≦0+3σ

[0818] 0−3σ≦δ(Γ−Φ)_(i)≦0+3σ

[0819] Next, there will be described a compression-ring-missing test.Whether the cylinder indicated by the variable ‘i’ has thecompression-ring missing is judged by judging whether all the followingexpressions are satisfied (see FIG. 80), i.e., are correct (“TRUE”):

[0820] 0+3σ≦δP_(EXmaxi)

[0821] 0+3σ≦δP_(EXconsti)

[0822] 0−3σ≦δΓ_(i)≦0+3σ

[0823] 0−3σ≦δΣ_(i)≦0+3σ

[0824] 0−3σ≦δΦ_(i)≦0+3σ

[0825] 0−3σ≦δΛ_(i)≦0+3σ

[0826] 0−3σ≦δΨ_(i)≦0+3σ

[0827] 0−3σ≦δ(Γ−Φ)_(i)≦0+3σ

[0828] The group of expressions employed in each of the above-describedfault finding tests can provide a correct conclusion so long as acertain assumption is correct. This assumption is that the respectiveabsolute values of the values other than zero indicated in the tables ofFIGS. 79 and 80 are sufficiently greater than the values, 3σ, which arerepresentative of the substantial upper and lower limits of therespective ranges within which the eight parameters indicated in thetables change on normal engines. In other words, the assumption is thatthe range within which each of the eight parameters changes on engineswith faults does not overlap a corresponding range within which the eachparameter changes on normal engines. In the present embodiment, inalmost all cases, the respective absolute values of the values otherthan zero indicated in the tables of FIGS. 79 and 80 are greater thanthe values, 3σ. However, there are some exceptional cases. For example,the value of finite difference δP_(EXconsti), indicated in the table ofFIG. 80, corresponding to the compression-ring missing is the value, 1,that may be smaller than the value, 3σ, therefor. In those exceptionalcases, if the above-indicated expression relating to the finitedifference δP_(EXconsti) is used for finding the compression-ringmissing, the CPU may erroneously judge that the cylinder #i does nothave the compression-ring missing, notwithstanding the presence of thatfault. This problem is solved by not using, in those exceptional cases,the above-indicated expression relating to the finite differenceδP_(EXconsti). This applies to the other, seven parameters. Withouttaking the value of finite difference δP_(EXconsti) into account, theCPU can accurately identify, based on the respective values of the otherparameters indicated in the table of FIG. 80, the fault ofcompression-ring missing from the other faults or the normal assembledstate of the engine 90. It is noted that there are some cases where itis redundant to use, for finding each fault, all of the corresponding,above-indicated expressions. For example, it is apparent from FIGS. 79and 80 that the respective values of finite difference δΓ_(i)corresponding to all the faults are equal to those of finite differenceδΨ_(i). Therefore, it is possible to omit the step or steps relating toeither one of the two parameters.

[0829]FIG. 81 is a flow chart representing an engine testing programwhich is pre-stored in the ROM of the fault finder 117 shown in FIG. 4and is carried out by the CPU and the RAM of the finder 117. Thisprogram is carried out for performing the above-described seventh enginetesting method in accordance with the present invention. According tothis program, the presence or absence of each of the faults indicated inthe tables of FIGS. 79 and 80 is identified by using the corresponding,above-indicated group of expressions. More specifically described, atSteps U1100, U1102, U1104, U1106, U1108, U1110, U1112, and U1114, therespective values of eight parameters δP_(EXmaxi), δP_(EXconsti),δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ) are used, respectively,for judging, for identifying the presence or absence of each of thefaults, whether the corresponding, above-indicated group of expressionsare correct (“TRUE”). In the case where a certain group of expressionscorresponding to a certain fault all provide the “TRUE” judgments atSteps U1100 to U1114, the CPU judges that the engine 90 has that fault.In this case, the control of the CPU goes to Step U1116 to command thedisplay 118 to light the lamp corresponding to the fault thus identifiedor specified. Then, the CPU quits the present routine.

[0830] However, as described above, the CPU omits a certain step whenthe CPU tries to find a certain fault. For example, when the CPU triesto find the small exhaust-valve clearance, the CPU omits Step U1100 atwhich the value of finite difference δP_(EXmaxi) is used.

[0831] On the other hand, if at least one of Steps U1100 to U1114provides the “FALSE” judgment, the CPU directly quits the presentroutine without performing any additional operation. The present routineis carried out, for each of the faults, by using the corresponding,above-indicated group of expressions. It is noted that as is apparentfrom FIG. 79, it is impossible to identify the one-tooth fast state ofthe left cam pulley 24 or the left driven gear 40 from the one-toothslow state of the right cam pulley 26 or the right driven gear 42, oridentify the one-tooth slow state of the left cam pulley 24 or the leftdriven gear 40 from the one-tooth fast state of the right cam pulley 26or the right driven gear 42. Therefore, the CPU can only judge that theengine 90 has either one of the former two faults, or that the engine 90has either one of the latter two faults.

[0832] The routine of FIG. 81 may be used for judging only whether theengine 90 is normal or not. In this case, the following group ofexpressions are employed:

[0833] 0−3σ≦δP_(EXmaxi)≦0+3σ

[0834] 0−3σ≦P_(EXconsti)≦0+3σ

[0835] 0−3σ≦δΓ_(i)≦0+3σ

[0836] 0−3σ≦δΣ_(i)≦0+3σ

[0837] 0−3σ≦δΦ_(i)≦0+3σ

[0838] 0−3σ≦δΛ_(i)≦0+3σ

[0839] 0−3σ≦δΨ_(i)≦0+3σ

[0840] 0−3σ≦δ(Γ−Φ)_(i)≦0+3σ

[0841] In this case, Step U1116 is modified such that the CPU commandsthe display 118 to light the OK lamp 200 indicating that the engine 90is normal.

[0842] It emerges from the foregoing description that the routine ofFIG. 81 needs measuring the respective values of parameters δP_(EXmaxi),δP_(EXconsti), δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ) from aplurality of normal engines and determining, based on the measuredvalues, the respective standard deviations, σ, of those parameters.Those operations may be omitted by modifying the routine of FIG. 81 asdescribed below.

[0843] First, when the cam-pulley test or the driven-gear test iscarried out, the steps at which the values of parameters δP_(EXmaxi),δP_(EXconsti), δΛ_(i) are used are omitted, that is, Steps U1100, U1102,U1110 of FIG. 81 are omitted. In other words, only the values ofparameters δΓ_(i), δΣ_(i), δΦ_(i), δΨ_(i), δ(Γ−Φ) are used. Those valuesare theoretically known without having to measure actually on an engine.For example, in the case where an engine has the one-tooth fast or slowstate of the cam pulley 24, 26, the parameters δΓ_(i), δΣ_(i), δΦ_(i),δΨ_(i) change by +15 or −15. This is theoretically known. On the otherhand, the values of parameters δP_(EXmaxi), δP_(EXconsti), δΛ_(i) can beknown by actual measurement from an assembled engine only. Therefore,those steps at which the values of parameters δP_(EXmaxi),δP_(EXconsti), δΛ_(i) are used are omitted.

[0844] Next, when the small- or large-intake-valve-clearance test or thesmall-exhaust-valve-clearance test is carried out, the routine of FIG.81 is modified so as to use the respective signs of the values ofparameters δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ). As far as thepresent embodiment concerned, the “signs” are defined as including asign indicating values about zero, in addition to the positive andnegative signs. For example, values about zero are defined as falling inthe about-zero range of 0±2. Those values, ±2, are values which areempirically known, and are not values which are directly derived fromthe values measured from the individual engine 90 being tested.Different about-zero ranges may be used for the different parametersδΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ), respectively. Hence,values having the positive sign are defined as being not smaller than 2,and values having the negative sign are defined as being not greaterthan −2. The respective absolute values of the values indicated in thetable of FIG. 80 cannot be known unless actual measurements are carriedout on engines with faults. However, in many cases, the respective signs(i.e., positive, negative, or about zero) of values of parametersδΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ) can be theoreticallyknown from information about the structure, etc. of the engine 90. Inthe table of FIG. 80, the respective signs (i.e., positive, negative, orabout zero) of values of parameters δΓ_(i), δΣ_(i), δΦ_(i), δΛ_(i),δΨ_(i), δ(Γ−Φ) which are utilized for finding the above-indicated threefaults, are indicated. In addition, the table of FIG. 80 indicates thesign (i.e., negative) of value of parameter δP_(EXmaxi) which isutilized for finding the large exhaust-valve clearance, and the sign(i.e., positive) of value of parameter δP_(EXmaxi) which is utilized forfinding the compression-ring missing, as described later.

[0845] When the small-intake-valve-clearance test is carried out, StepsU11OO and U1102 of FIG. 81 are omitted like when the cam-pulley test orthe driven-gear test is carried out. In addition, Steps U1104 to U1114are modified so as to judge whether the following expressions arecorrect (“TRUE”) or not (“FALSE”), respectively:

[0846] δΓ_(i)≦2 (U1104)

[0847] δΣ_(i)˜0 (U1106)

[0848] δΦ_(i)˜0 (U1108)

[0849] δΛ_(i)≧2 (U1110)

[0850] δΨ_(i)≧2 (U1112)

[0851] δ(Γ−Φ)_(i)≦−2 (U1114)

[0852] In the above expressions, for example, δΓ_(i)≦2 means that thevalue of finite difference δΓ_(i) is greater than about zero (i.e.,positive); δΣ_(i)˜0 means that the value of finite difference δΣ_(i) isabout zero; and δ(Γ−Φ)_(i)≦−2 means that the value of parameterδ(Γ−Φ)_(i) is smaller than about zero (i.e., negative).

[0853] When the large-intake-valve-clearance test is carried out, StepsU1104 to U1114 are modified so as to judge whether the followingexpressions are correct (“TRUE”) or not, respectively:

[0854] δΓ_(i)≦−2 (U1104)

[0855] δΣ_(i)˜0 (U1106)

[0856] δΦ_(i)˜0 (U1108)

[0857] δΛ_(i)≦−2 (U1110)

[0858] δΨ_(i)≦−2 (U1112)

[0859] δ(Γ−Φ)_(i)≧2 (U1114)

[0860] When the small-exhaust-valve-clearance test is carried out, StepsU1104 to U1114 are modified so as to judge whether the followingexpressions are correct (“TRUE”) or not, respectively:

[0861] δΓ_(i)˜0 (U1104)

[0862] δΣ_(i)≦−2 (U1106)

[0863] δΦ_(i)≧2 (U1108)

[0864] δΛ_(i)˜0 (U1110)

[0865] δΨ_(i)˜0 (U1112)

[0866] δ(Γ−Φ)_(i)≧2 (U1114)

[0867] When the large-exhaust-valve-clearance test or thecompression-ring missing test is carried out, Step U1100 is not omitted.That is, only Step U1102 is omitted. More specifically described, whenthe large-exhaust-valve-clearance test is carried out, Steps U1100 andU1104 to U1114 are modified so as to judge whether the followingexpressions are correct (“TRUE”) or not, respectively:

[0868] δP_(EXmax)≦−2 (U1100)

[0869] δΓ_(i)˜0 (U1104)

[0870] δΣ_(i)˜0 (U1106)

[0871] δΦ_(i)˜0 (U1108)

[0872] δΛ_(i)˜0 (U1110)

[0873] δΨ_(i)˜0 (U1112)

[0874] δ(Γ−Φ)_(i)˜0 (U1114)

[0875] When the compression-ring missing test is carried out, StepsU1100 and U1104 to U1114 are modified so as to judge whether thefollowing expressions are correct (“TRUE”) or not, respectively:

[0876] δP_(EXmax)≦2 (U1100)

[0877] δΓ_(i)˜0 (U1104)

[0878] δΣ_(i)˜0 (U1106)

[0879] δΦ_(˜0) (U1108)

[0880] δΛ_(i)˜0 (U1110)

[0881] δΨ_(i)˜0 (U1112)

[0882] δ(Γ−Φ)_(i)˜0 (U1114)

[0883] If the routine of FIG. 81 is modified as indicated above, each ofthe faults can be identified without having to determine, in advance,the standard deviations, a, of parameters based on the values ofparameters measured from normal engines.

[0884] As is apparent from the foregoing description, in the seventhengine testing method, each of the faults is identified by comparing thevalues obtained from one cylinder of each pair of successively ignitedcylinders, with the values obtained from the other cylinder of the eachpair. As far as the engine 90 having the left and right banks isconcerned, it can be said that each fault is identified based on thecomparison between the values obtained from one cylinder (variable ‘i’is an odd number) of the left bank and with the values obtained from onecylinder (variable ‘i’ is an even number) of the right bank.

[0885] Even in the case where one or more different types of enginesthan the engine 90 are tested, the values of parameters δΓ_(i), δΣ_(i),δΦ_(i), δΛ_(i), δΨ_(i), δ(Γ−Φ) may have, for each of the faults, thesame signs (i.e., positive, negative, or about zero) as indicated in thetable of FIG. 80. In the latter case, the present method may be used fortesting more than two types of engines.

[0886] In each of the sixth and seventh embodiments, the respectivevalues of parameters P_(EXmax), ΔΓ_(i), etc. obtained from one cylinderand the value or values calculated based on those respective values arecompared with the respective values of parameters P_(EXmax), ΔΓ_(i),etc. obtained from another cylinder and the value or values calculatedbased on those respective values. Therefore, it is not needed todetermine the respective CS angles when the exhaust pressures P_(EX) andthe intake pressure P_(IN) satisfy the predetermined conditions.Therefore, the CS sensor 114 shown in FIG. 4 may be omitted in actualengine tests. Thus, the testing apparatus shown in FIG. 4 can enjoy asimpler construction.

[0887] In each of the sixth and seventh embodiments, the intake pressureP_(IN) is detected from the surge tank 96. However, an intake pressureP_(IN) may be detected from each of the intake ports 92. In the lattercase, the intake pressures P_(IN) corresponding to all the cylinders #1to #6 are obtained, and the assembling faults of the engine 90 areidentified based on those intake pressures P_(IN), In addition, in eachof the sixth and seventh embodiments, the intake-valve side space isprovided by the respective inner spaces of the surge tank 96, the intakemanifolds 94, and the intake ports 92. However, six intake-valve sidespaces may be provided by the respective inner spaces of the six intakeports 92. In the last case, those intake-valve side spaces are closed inaddition to, or in place of, one or more exhaust-valve side spaces,while the sixth or seventh engine testing method is carried out.

[0888] In the case where six intake-valve side spaces are provided bythe respective inner spaces of the six intake ports 92, the CPU candetermine, from each of the six intake pressures P_(IN), intake-pressurevalues corresponding to the exhaust-pressure maximal value P_(EXmax),the exhaust-pressure constant value P_(EXmax), etc., and determine angledifferences corresponding to the exhaust-pressure decrease-start-anglerelative difference ΔΦ_(i), etc. Therefore, the CPU can identify eachfault based on those intake-pressure values and those angle differences.

[0889] In each of the sixth and seventh embodiments, the V6 DOHCgasoline engines are tested. However, the present invention isapplicable to the testing of various types of engines. For example, inthe case where SOHC engines are tested, the testing steps for findingthe fault with the driven gears 40, 42 are omitted. In addition, in thecase where DOHC engines of the type wherein intake cam shafts (32, 34)are driven by not driven gears (40, 42) but different cam pulleys,testing steps for finding a fault with those different cam pulleys maybe employed in place of the testing steps for finding the fault with thedriven gears. Meanwhile, in each of the sixth and seventh embodiments,the engine test is carried out based on parameters (e.g., theexhaust-pressure maximal-value-angle relative difference ΔΓ) derivedfrom the characteristic parameters of the exhaust pressures P_(EX) suchas the exhaust-pressure maximal values P_(EXmax), the exhaust-pressuremaximal-value angles Θ_(EXmax), etc. However, the other parametersindicated in the table of FIG. 24 and/or the other characteristicparameters of the curves shown in the graphs of FIG. 8, etc. may beemployed for the same purpose. For example, the maximum slope of thecurve shown in FIG. 8, or the crank-shaft angle corresponding to themaximum slope, the length and/or position of the interval in which therate of change of the curve is greater than a reference value, etc. maybe taken into account for finding a fault or faults with an engine. Thepresent invention may be also applicable to diesel engines.

[0890] In order to specify or identify, with higher reliability, each ofa plurality of faults which simultaneously occur to a single engine, theengine testing apparatus can gather more information from the engine.For example, all possible combinations of presence or absence ofpredetermined faults are artificially created on an engine, and thetesting apparatus gathers a group of respective values of predeterminedparameters P_(EXmax), ΔΓ_(i), ΔΦ_(i), etc. in each of all thecombinations of the predetermined faults created on the engine. Then,the testing apparatus obtains a group of respective values of thepredetermined parameters P_(EXmax), Θ_(EXmax), etc. from an engine beingtested, compares the obtained group of values with each of the referencegroups of values gathered in advance in all the fault combinations, andselects one of all the fault combinations which corresponds to thereference group most approximate to the obtained group, as the specifiedfault combination of the engine. In each of the sixth and seventhembodiments, the testing apparatus finds the one-tooth fast or slowstate of the crank pulley 20, the cam pulley 24, 26, or the driven gear40, 42. However, the testing apparatus may be adapted to find the two ormore teeth fast or slow state of each pulley 20, 24, 26, 40, 42. In thelast case, each parameter P_(EXmax), ΔΓ_(i), ΔΦ_(i), etc. may be dividedinto more ranges for finding a fault or faults with higher accuracy. Inthis case, slight differences of respective values of each parametermust be distinguished from each other. Since the engine testingapparatus employed in each of the sixth and seventh embodiments canquickly obtain a number of values of each parameter, it can find a faultor faults with an engine with high reliability by, e.g., statisticallyanalyzing those values.

1. A method of testing an assembled internal combustion engine having anintake valve (50) and an exhaust valve (48), characterized by rotatingthe assembled engine, measuring a timing of occurrence of at least onepredetermined condition of a pressure in at least one of an externalintake-valve side space (92) which communicates with the intake valveand an external exhaust-valve side space (100) which communicates withthe exhaust valve, and judging, based on the measured timing, whetherthere is at least one fault with the assembling of the engine.
 2. Amethod according to claim 1, wherein the judging step comprisescomparing the measured timing with a reference timing and judging, basedon the comparison result, whether there is at least one fault with theassembling of the engine.
 3. A method according to claim 1 or claim 2,wherein the measuring step comprises measuring at least one of a firsttiming when the exhaust pressure in the exhaust-valve side space takes amaximal value; a second timing when the exhaust pressure changes from afirst decreasing state to a constant state in which the exhaust pressuredoes not change as time elapses; a third timing when the exhaustpressure changes from the constant state to a second decreasing state; afourth timing when the intake pressure in the intake-valve side spacetakes a maximal value; and a fifth timing when the intake pressurechanges from a constant state in which the intake pressure does notchange as time elapses, to an increasing state.
 4. A method according toclaim 3, wherein the judging step comprises identifying at least onefault with the assembling of the engine based on at least one of apositive or negative sign and an absolute value of a difference betweenat least one measured timing out of the first to fifth timings and acorresponding one of a first, a second, a third, a fourth, and a fifthreference timing.
 5. A method according to claim 3 or claim 4, whereinthe judging step comprises identifying at least one fault with theassembling of the engine based on a combination of a plurality ofmeasured timings out of the first to fifth timings each of whichmeasured timings is different from a corresponding one of a first, asecond, a third, a fourth, and a fifth reference timing.
 6. A methodaccording to any one of claims 1 to 5, wherein the at least one faultcomprises at least one of an incorrect clearance of the intake valve; anincorrect clearance of the exhaust valve; an incorrect relative phasebetween a crank shaft (18) and a cam shaft (28, 30, 32, 34); and amissing of a compression ring (136, 138).
 7. A method according to claim6, wherein the incorrect relative phase between the crank shaft and thecam shaft comprises at least one of an incorrect relative phase betweenthe crank shaft and a crank pulley (20); an incorrect relative phasebetween a cam pulley (24, 26) and the cam shaft; and an incorrectrelative phase between a drive gear (36, 38) and a driven gear (40, 42).8. A method according to any one of claims 1 to 7, further comprisingthe step of closing at least one of an exhaust-valve side passage whichconnects between the exhaust valve and an exhaust manifold (250) and anintake-valve side passage which connects between the intake valve and anintake manifold (94), wherein the at least one of the externalexhaust-valve side space and the external intake-valve side spacecomprises at least one of an exhaust-valve side portion of the closedexhaust-valve side passage and an intake-valve side portion of theclosed intake-valve side passage.
 9. A method according to any one ofclaims 1 to 7, wherein the at least one of the external intake-valveside space and the external exhaust-valve side space comprises theexhaust-valve side space which comprises an exhaust-valve room (100) andan exhaust manifold (250) whose outlet is closed.
 10. A method accordingto any one of claims 1 to 7, wherein the at least one of the externalintake-valve side space and the external exhaust-valve side spacecomprises an internal space of a surge tank (96).
 11. A method accordingto any one of claims 1 to 10, wherein the judging step comprisesidentifying at least two faults out of a plurality of faults of theengine which result from the assembling thereof.
 12. A method accordingto any one of claims 1 to 11, wherein the at least one predeterminedcondition of the pressure can occur at a plurality of timingscorresponding to a plurality of faults which can result from theassembling of the engine, and wherein the judging step comprisesidentifying at least one of the plurality of faults, based on at leastone of (a) an amount of deviation of the measured timing of the at leastone predetermined condition from a reference timing and (b) acombination of at least two predetermined conditions whose measuredtimings are deviated from at least two reference timings, respectively.13. A method according to claim 12, further comprising the step ofdeciding, when a measured timing of each of at least two predeterminedconditions of the pressure is equal to a reference timing, that there isno fault with the assembling of the engine, and omitting carrying outthe judging step.
 14. A method according to claim 12 or claim 13,wherein the plurality of timings comprise at least one timing whichcorresponds to each of at least two faults of the plurality of faults,and wherein the identifying step comprises utilizing one of theplurality of timings which corresponds to a smallest number of faults,prior to the other timings.
 15. A method according to any one of claims12 to 14, wherein the identifying step comprises utilizing one of theplurality of timings which corresponds to at least one fault theidentification of which is most easily confirmed by an an operator,prior to the other timings.
 16. A method according to any one of claims12 to 15, wherein the identifying step comprises utilizing one of theplurality of timings which corresponds to at least one fault which ismost easily corrected by an operator, prior to the other timings.
 17. Amethod according to any one of claims 1 to 16, wherein the rotating stepcomprises rotating, using an independent rotating device, a crank shaftof the assembled engine and thereby reciprocating a piston of the enginein a cylinder of the engine, while said at least one of the intake-valveside and exhaust-valve side spaces is isolated from an atmosphere, andwherein the judging step comprises judging whether there is at least onefault with an assembled state of the engine, based on at least one of(a) a pressure in said one of the intake-valve side and exhaust-valveside spaces which is measured while a corresponding one of the intakeand exhaust valves is closed and (b) at least one of a starting and anending timing of a closed state of one of the intake and exhaust valveswhich corresponds to said one of the intake-valve side and exhaust-valveside spaces.
 18. A method according to any one of claims 1 to 17,wherein the assembled engine includes a plurality of cylinders each ofwhich has an intake valve (50) and an exhaust valve (48), wherein themeasuring step comprises measuring, for each of at least two cylindersof said plurality of cylinders, at least one of (a) a value of apressure in at least one of an external intake-valve side space (92)which communicates with the intake valve corresponding to said eachcylinder and an external exhaust-valve side space (100) whichcommunicates with the exhaust valve corresponding to said each cylinder,when said pressure satisfies said at least one predetermined condition,and (b) a timing at which said pressure satisfies said at least onepredetermined condition, wherein the method further comprises a step ofcomparing the at least one of the value and the timing of a first one ofsaid at least two cylinders with the at least one of the value and thetiming of a second one of said at least two cylinders, and wherein thejudging step comprises judging that there is at least one fault with theassembling of the engine, when the at least one of the value and thetiming of said first cylinder is not equal to the at least one of thevalue and the timing of said second cylinder.
 19. A method of testing anengine including a cylinder, a piston (10, 12), a crank shaft (18), anintake valve (50) and an exhaust valve (48), characterized by rotating,using an independent rotating device, the crank shaft and therebyreciprocating the piston in the cylinder, while at least one of anexternal intake-valve side space (92) which communicates with the intakevalve and an external exhaust-valve side space (100) which communicateswith the exhaust valve is isolated from an atmosphere, and evaluating astate of the engine based on at least one of (a) a pressure in said oneof the intake-valve side and exhaust-valve side spaces which is measuredwhile a corresponding one of the intake and exhaust valves is closed and(b) at least one of a starting and an ending timing of a closed state ofone of the intake and exhaust valves which corresponds to said one ofthe intake-valve side and exhaust-valve side spaces.
 20. A method oftesting an assembled internal combustion engine including a plurality ofcylinders each of which has an intake valve (50) and an exhaust valve(48), characterized by rotating the assembled engine, measuring, foreach of at least two cylinders of said plurality of cylinders, at lestone of (a) a value of a pressure in at least one of an externalintake-valve side space (92) which communicates with the intake valvecorresponding to said each cylinder and an external exhaust-valve sidespace (100) which communicates with the exhaust valve corresponding tosaid each cylinder, when said pressure satisfies a predeterminedcondition, and (b) a timing at which said pressure satisfies saidpredetermined condition, comparing the at least one of the value and thetiming of a first one of said at least two cylinders with the at leastone of the value and the timing of a second one of said at least twocylinders, and judging that there is at least one fault with theassembling of the engine, when the at least one of the value and thetiming of said first cylinder is not equal to the at least one of thevalue and the timing of said second cylinder.